Implement a better fix for unsetting special env vars #7

JohnoKing · 2020-06-13T12:39:14Z

The regression this pull request fixes was first introduced in ksh93t 2008-07-25. It was previously worked around in 6f0e008 by forking subshells if any special environment variable is unset.

The reason why (unset LC_NUMERIC; LC_NUMERIC=invalid) works as expected in ksh93s+ is because when unall() calls sh_assignok() the second argument doesn't set NV_MOVE, as that version never moves nodes, it only clones them. sh_assignok(np,0) is similar to sh_assignok(np,1) in ksh93s+ (link):

	sh.subshell = 0;;
	mp->nvname = np->nvname;
	nv_clone(np,mp,NV_NOFREE);
	sh.subshell = save;
	return(np);

In ksh93t and higher, setting the second argument to zero causes the node to be moved with NV_MOVE, which causes the discipline function associated with the variable node to be removed when np->nvfun is set to zero (i.e. NULL):

ksh/src/cmd/ksh93/sh/subshell.c

Lines 301 to 305 in 289f56c

    
           if(nv_isattr(np,NV_NOFREE)) 
        
           	nv_onattr(mp,NV_IDENT); 
        
           nv_clone(np,mp,(add?(nv_isnull(np)?0:NV_NOFREE)|NV_ARRAY:NV_MOVE)); 
        
           shp->subshell = save; 
        
           return(np);

ksh/src/cmd/ksh93/sh/nvdisc.c

Lines 961 to 965 in 289f56c

    
           if(flags&NV_MOVE) 
        
           { 
        
           	if(nv_isattr(np,NV_INTEGER)) 
        
           		mp->nvalue.ip = np->nvalue.ip; 
        
           	np->nvfun = 0;

This patch fixes the problem by cloning the node with sh_assignok() if it is a special variable with a discipline function. This allows special variables to work as expected in virtual subshells. The original workaround has been kept for the $PATH variable only, as hash tables are still broken in virtual subshells. It has been updated accordingly to only fork subshells if it detects the variable node for PATH. I have added two more regression tests for changing the PATH in subshells to make sure hash tables continue working as expected with this fix.

McDutchie

Thank you for the pull request, the documentation, and the history! Where does one find these ancient ksh sources?

~~Meanwhile, I have a question… see the comment below.~~ Never mind. Clearly, I'm too tired to think straight. I'm going to leave this until I've got some sleep.

The regression this commit fixes was first introduced in ksh93t 2008-07-25. It was previously worked around in 6f0e008 by forking subshells if any special environment variable is unset. The reason why this problem doesn't occur in ksh93s+ is because in that version of ksh sh_assignok never moves nodes, it only clones them. The second argument doesn't set NV_MOVE, which makes `sh_assignok(np,0)` is similar to `sh_assignok(np,1)`. In ksh93t and higher, setting the second argument to zero causes the node to be moved with NV_MOVE, which causes the discipline function associated with the variable node to be removed when `np->nvfun` is set to zero (i.e. NULL). This is why a command like `(unset LC_NUMERIC; LC_NUMERIC=invalid)` doesn't print a diagnostic, as it looses its discipline function. This patch fixes the problem by cloning the node with sh_assignok if it is a special variable with a discipline function. This allows special variables to work as expected in virtual subshells. The original workaround has been kept for the $PATH variable only, as hash tables are still broken in virtual subshells. It has been updated accordingly to only fork subshells if it detects the variable node for PATH. I have added two more regression tests for changing the PATH in subshells to make sure hash tables continue working as expected with this fix. src/cmd/ksh93/bltins/typeset.c: - Only fork virtual subshells if the PATH will be changed. If a variable is a special variable with a discipline function, it should be just be cloned, not moved. src/cmd/ksh93/sh/nvdisc.c: - Add a comment to clarify that NV_MOVE will delete the discipline function associated with the node. src/cmd/ksh93/tests/subshells.sh: - Add two more regression tests for unsetting the PATH in subshells, one for if PATH is being pointed to by a nameref. Condense the hash table tests by moving the main test into a single function.

Since we now have a shiny new POSIX compliant 'times' builtin, we might as well use it. src/cmd/ksh93/tests/shtests: - Run 'times' at end of test run. - Skip the pretty-printing until ksh93#7 is fixed. (cherry picked from commit 2c27d9fbc239583004ec70377db98627eea5e294)

I didn't trust this back in e3d7bf1 (which disabled it for interactive shells) and I trust it less now. In af6a32d/6b380572, this was also disabled for virtual subshells as it caused program flow corruption there. Now, on macOS 10.14.6, a crash occurs when repeatedly running a command with this optimisation: $ ksh -c 'for((i=0;i<100;i++));do print -n "$i ";(sleep 1&);done' 0 1 2 3 4 5 6 7 Illegal instruction Oddly enough it seems that I can only reproduce this crash on macOS -- not on Linux, OpenBSD, or Solaris. It could be a macOS bug, particularly given the odd message in the stack trace below. I've had enough, though. Out it comes. Things now work fine, the reproducer is fixed on macOS, and it didn't optimise much anyway. The double-fork issue discussed in e3d7bf1 remains. ________ For future reference, here's an lldb debugger session with a stack trace. It crashes on calling calloc() (via sh_calloc(), via sh_newof()) in jobsave_create(). This is not an invalid pointer problem as we're allocating new memory, so it does look like an OS bug. The "BUG IN CLIENT OF LIBPLATFORM" message is interesting. $ lldb -- arch/*/bin/ksh -c 'for((i=0;i<100;i++));do print -n "$i ";(sleep 1&);done' (lldb) target create "arch/darwin.i386-64/bin/ksh" Current executable set to 'arch/darwin.i386-64/bin/ksh' (x86_64). (lldb) settings set -- target.run-args "-c" "for((i=0;i<100;i++));do print -n \"$i \";(sleep 1&);done" (lldb) run error: shell expansion failed (reason: lldb-argdumper exited with error 2). consider launching with 'process launch'. (lldb) process launch Process 35038 launched: '/usr/local/src/ksh93/ksh/arch/darwin.i386-64/bin/ksh' (x86_64) 0 1 2 3 4 5 6 7 8 9 Process 35038 stopped * thread #1, queue = 'com.apple.main-thread', stop reason = EXC_BAD_INSTRUCTION (code=EXC_I386_INVOP, subcode=0x0) frame #0: 0x00007fff70deb1c2 libsystem_platform.dylib`_os_unfair_lock_recursive_abort + 23 libsystem_platform.dylib`_os_unfair_lock_recursive_abort: -> 0x7fff70deb1c2 <+23>: ud2 libsystem_platform.dylib`_os_unfair_lock_unowned_abort: 0x7fff70deb1c4 <+0>: movl %edi, %eax 0x7fff70deb1c6 <+2>: leaq 0x1a8a(%rip), %rcx ; "BUG IN CLIENT OF LIBPLATFORM: Unlock of an os_unfair_lock not owned by current thread" 0x7fff70deb1cd <+9>: movq %rcx, 0x361cb16c(%rip) ; gCRAnnotations + 8 Target 0: (ksh) stopped. (lldb) bt * thread #1, queue = 'com.apple.main-thread', stop reason = EXC_BAD_INSTRUCTION (code=EXC_I386_INVOP, subcode=0x0) * frame #0: 0x00007fff70deb1c2 libsystem_platform.dylib`_os_unfair_lock_recursive_abort + 23 frame #1: 0x00007fff70de7c9a libsystem_platform.dylib`_os_unfair_lock_lock_slow + 239 frame #2: 0x00007fff70daa3bd libsystem_malloc.dylib`tiny_malloc_should_clear + 188 frame #3: 0x00007fff70daa20f libsystem_malloc.dylib`szone_malloc_should_clear + 66 frame #4: 0x00007fff70dab444 libsystem_malloc.dylib`malloc_zone_calloc + 99 frame #5: 0x00007fff70dab3c4 libsystem_malloc.dylib`calloc + 30 frame #6: 0x000000010003fa5d ksh`sh_calloc(nmemb=1, size=16) at init.c:264:13 frame #7: 0x000000010004f8a6 ksh`jobsave_create(pid=35055) at jobs.c:272:8 frame #8: 0x000000010004ed42 ksh`job_reap(sig=20) at jobs.c:363:9 frame #9: 0x000000010004ff6f ksh`job_waitsafe(sig=20) at jobs.c:511:3 frame #10: 0x00007fff70de9b5d libsystem_platform.dylib`_sigtramp + 29 frame #11: 0x00007fff70d39ac4 libsystem_kernel.dylib`__fork + 12 frame #12: 0x00007fff70c57d80 libsystem_c.dylib`fork + 17 frame #13: 0x000000010009590d ksh`sh_exec(t=0x0000000101005d30, flags=4) at xec.c:1883:16 frame #14: 0x0000000100096013 ksh`sh_exec(t=0x0000000101005d30, flags=4) at xec.c:2019:4 frame #15: 0x0000000100096c4f ksh`sh_exec(t=0x0000000101005a40, flags=5) at xec.c:2213:9 frame #16: 0x0000000100096013 ksh`sh_exec(t=0x0000000101005a40, flags=5) at xec.c:2019:4 frame #17: 0x000000010001c23f ksh`exfile(iop=0x0000000100405750, fno=-1) at main.c:603:4 frame #18: 0x000000010001b23c ksh`sh_main(ac=3, av=0x00007ffeefbff4f0, userinit=0x0000000000000000) at main.c:365:2 frame #19: 0x0000000100000776 ksh`main(argc=3, argv=0x00007ffeefbff4f0) at pmain.c:45:9 frame #20: 0x00007fff70bfe3d5 libdyld.dylib`start + 1

The ASan crash in basic.sh when sourcing multiple files is caused by a bug that is similar to the crash fixed in 59a5672. This is the trace for the regression test crash (note that in order to see the trace, the 2>/dev/null redirect must be disabled): ==1899388==ERROR: AddressSanitizer: heap-use-after-free on address 0x6150000005b0 at pc 0x55a5e3f9432a bp 0x7ffeb91ea110 sp 0x7ffeb91ea100 WRITE of size 8 at 0x6150000005b0 thread T0 #0 0x55a5e3f94329 in funct /home/johno/GitRepos/KornShell/ksh/src/cmd/ksh93/sh/parse.c:967 ksh93#1 0x55a5e3f96f77 in item /home/johno/GitRepos/KornShell/ksh/src/cmd/ksh93/sh/parse.c:1349 ksh93#2 0x55a5e3f90c9f in term /home/johno/GitRepos/KornShell/ksh/src/cmd/ksh93/sh/parse.c:642 ksh93#3 0x55a5e3f90ac1 in list /home/johno/GitRepos/KornShell/ksh/src/cmd/ksh93/sh/parse.c:613 ksh93#4 0x55a5e3f90845 in sh_cmd /home/johno/GitRepos/KornShell/ksh/src/cmd/ksh93/sh/parse.c:561 ksh93#5 0x55a5e3f909e0 in sh_cmd /home/johno/GitRepos/KornShell/ksh/src/cmd/ksh93/sh/parse.c:586 ksh93#6 0x55a5e3f8fd5e in sh_parse /home/johno/GitRepos/KornShell/ksh/src/cmd/ksh93/sh/parse.c:438 ksh93#7 0x55a5e3fc43c1 in sh_eval /home/johno/GitRepos/KornShell/ksh/src/cmd/ksh93/sh/xec.c:635 ksh93#8 0x55a5e4012172 in b_dot_cmd /home/johno/GitRepos/KornShell/ksh/src/cmd/ksh93/bltins/misc.c:318 ksh93#9 0x55a5e3fca3cb in sh_exec /home/johno/GitRepos/KornShell/ksh/src/cmd/ksh93/sh/xec.c:1254 ksh93#10 0x55a5e3fd01d4 in sh_exec /home/johno/GitRepos/KornShell/ksh/src/cmd/ksh93/sh/xec.c:1932 ksh93#11 0x55a5e3fc4544 in sh_eval /home/johno/GitRepos/KornShell/ksh/src/cmd/ksh93/sh/xec.c:651 ksh93#12 0x55a5e4012172 in b_dot_cmd /home/johno/GitRepos/KornShell/ksh/src/cmd/ksh93/bltins/misc.c:318 ksh93#13 0x55a5e3fca3cb in sh_exec /home/johno/GitRepos/KornShell/ksh/src/cmd/ksh93/sh/xec.c:1254 ksh93#14 0x55a5e3ecc1cd in exfile /home/johno/GitRepos/KornShell/ksh/src/cmd/ksh93/sh/main.c:604 ksh93#15 0x55a5e3ec9e7f in sh_main /home/johno/GitRepos/KornShell/ksh/src/cmd/ksh93/sh/main.c:369 ksh93#16 0x55a5e3ec801d in main /home/johno/GitRepos/KornShell/ksh/src/cmd/ksh93/sh/pmain.c:41 ksh93#17 0x7f637b4db2cf (/usr/lib/libc.so.6+0x232cf) ksh93#18 0x7f637b4db389 in __libc_start_main (/usr/lib/libc.so.6+0x23389) ksh93#19 0x55a5e3ec7f24 in _start ../sysdeps/x86_64/start.S:115 Code in question: https://github.com/ksh93/ksh/blob/8d57369b0cb39074437dd82924b604155e30e1e0/src/cmd/ksh93/sh/parse.c#L963-L968 To avoid any more similar crashes, all of the fixes introduced in 7e317c5 that set slp->slptr to null have been improved with the fix in 59a5672.

The ASan crash in basic.sh when sourcing multiple files is caused by a bug that is similar to the crash fixed in 59a5672. This is the trace for the regression test crash (note that in order to see the trace, the 2>/dev/null redirect must be disabled): ==1899388==ERROR: AddressSanitizer: heap-use-after-free on address 0x6150000005b0 at pc 0x55a5e3f9432a bp 0x7ffeb91ea110 sp 0x7ffeb91ea100 WRITE of size 8 at 0x6150000005b0 thread T0 #0 0x55a5e3f94329 in funct /home/johno/GitRepos/KornShell/ksh/src/cmd/ksh93/sh/parse.c:967 #1 0x55a5e3f96f77 in item /home/johno/GitRepos/KornShell/ksh/src/cmd/ksh93/sh/parse.c:1349 #2 0x55a5e3f90c9f in term /home/johno/GitRepos/KornShell/ksh/src/cmd/ksh93/sh/parse.c:642 #3 0x55a5e3f90ac1 in list /home/johno/GitRepos/KornShell/ksh/src/cmd/ksh93/sh/parse.c:613 #4 0x55a5e3f90845 in sh_cmd /home/johno/GitRepos/KornShell/ksh/src/cmd/ksh93/sh/parse.c:561 #5 0x55a5e3f909e0 in sh_cmd /home/johno/GitRepos/KornShell/ksh/src/cmd/ksh93/sh/parse.c:586 #6 0x55a5e3f8fd5e in sh_parse /home/johno/GitRepos/KornShell/ksh/src/cmd/ksh93/sh/parse.c:438 #7 0x55a5e3fc43c1 in sh_eval /home/johno/GitRepos/KornShell/ksh/src/cmd/ksh93/sh/xec.c:635 #8 0x55a5e4012172 in b_dot_cmd /home/johno/GitRepos/KornShell/ksh/src/cmd/ksh93/bltins/misc.c:318 #9 0x55a5e3fca3cb in sh_exec /home/johno/GitRepos/KornShell/ksh/src/cmd/ksh93/sh/xec.c:1254 #10 0x55a5e3fd01d4 in sh_exec /home/johno/GitRepos/KornShell/ksh/src/cmd/ksh93/sh/xec.c:1932 #11 0x55a5e3fc4544 in sh_eval /home/johno/GitRepos/KornShell/ksh/src/cmd/ksh93/sh/xec.c:651 #12 0x55a5e4012172 in b_dot_cmd /home/johno/GitRepos/KornShell/ksh/src/cmd/ksh93/bltins/misc.c:318 #13 0x55a5e3fca3cb in sh_exec /home/johno/GitRepos/KornShell/ksh/src/cmd/ksh93/sh/xec.c:1254 #14 0x55a5e3ecc1cd in exfile /home/johno/GitRepos/KornShell/ksh/src/cmd/ksh93/sh/main.c:604 #15 0x55a5e3ec9e7f in sh_main /home/johno/GitRepos/KornShell/ksh/src/cmd/ksh93/sh/main.c:369 #16 0x55a5e3ec801d in main /home/johno/GitRepos/KornShell/ksh/src/cmd/ksh93/sh/pmain.c:41 #17 0x7f637b4db2cf (/usr/lib/libc.so.6+0x232cf) #18 0x7f637b4db389 in __libc_start_main (/usr/lib/libc.so.6+0x23389) #19 0x55a5e3ec7f24 in _start ../sysdeps/x86_64/start.S:115 Code in question: https://github.com/ksh93/ksh/blob/8d57369b0cb39074437dd82924b604155e30e1e0/src/cmd/ksh93/sh/parse.c#L963-L968 To avoid any more similar crashes, all of the fixes introduced in 7e317c5 that set slp->slptr to null have been improved with the fix in 59a5672.

The ASan crash in basic.sh when sourcing multiple files is caused by a bug that is similar to the crash fixed in f24040e. This is the trace for the regression test crash (note that in order to see the trace, the 2>/dev/null redirect must be disabled): ==1899388==ERROR: AddressSanitizer: heap-use-after-free on address 0x6150000005b0 at pc 0x55a5e3f9432a bp 0x7ffeb91ea110 sp 0x7ffeb91ea100 WRITE of size 8 at 0x6150000005b0 thread T0 #0 0x55a5e3f94329 in funct /home/johno/GitRepos/KornShell/ksh/src/cmd/ksh93/sh/parse.c:967 #1 0x55a5e3f96f77 in item /home/johno/GitRepos/KornShell/ksh/src/cmd/ksh93/sh/parse.c:1349 #2 0x55a5e3f90c9f in term /home/johno/GitRepos/KornShell/ksh/src/cmd/ksh93/sh/parse.c:642 #3 0x55a5e3f90ac1 in list /home/johno/GitRepos/KornShell/ksh/src/cmd/ksh93/sh/parse.c:613 #4 0x55a5e3f90845 in sh_cmd /home/johno/GitRepos/KornShell/ksh/src/cmd/ksh93/sh/parse.c:561 #5 0x55a5e3f909e0 in sh_cmd /home/johno/GitRepos/KornShell/ksh/src/cmd/ksh93/sh/parse.c:586 #6 0x55a5e3f8fd5e in sh_parse /home/johno/GitRepos/KornShell/ksh/src/cmd/ksh93/sh/parse.c:438 #7 0x55a5e3fc43c1 in sh_eval /home/johno/GitRepos/KornShell/ksh/src/cmd/ksh93/sh/xec.c:635 #8 0x55a5e4012172 in b_dot_cmd /home/johno/GitRepos/KornShell/ksh/src/cmd/ksh93/bltins/misc.c:318 #9 0x55a5e3fca3cb in sh_exec /home/johno/GitRepos/KornShell/ksh/src/cmd/ksh93/sh/xec.c:1254 #10 0x55a5e3fd01d4 in sh_exec /home/johno/GitRepos/KornShell/ksh/src/cmd/ksh93/sh/xec.c:1932 #11 0x55a5e3fc4544 in sh_eval /home/johno/GitRepos/KornShell/ksh/src/cmd/ksh93/sh/xec.c:651 #12 0x55a5e4012172 in b_dot_cmd /home/johno/GitRepos/KornShell/ksh/src/cmd/ksh93/bltins/misc.c:318 #13 0x55a5e3fca3cb in sh_exec /home/johno/GitRepos/KornShell/ksh/src/cmd/ksh93/sh/xec.c:1254 #14 0x55a5e3ecc1cd in exfile /home/johno/GitRepos/KornShell/ksh/src/cmd/ksh93/sh/main.c:604 #15 0x55a5e3ec9e7f in sh_main /home/johno/GitRepos/KornShell/ksh/src/cmd/ksh93/sh/main.c:369 #16 0x55a5e3ec801d in main /home/johno/GitRepos/KornShell/ksh/src/cmd/ksh93/sh/pmain.c:41 #17 0x7f637b4db2cf (/usr/lib/libc.so.6+0x232cf) #18 0x7f637b4db389 in __libc_start_main (/usr/lib/libc.so.6+0x23389) #19 0x55a5e3ec7f24 in _start ../sysdeps/x86_64/start.S:115 Code in question: https://github.com/ksh93/ksh/blob/8d57369b0cb39074437dd82924b604155e30e1e0/src/cmd/ksh93/sh/parse.c#L963-L968 To avoid any more similar crashes, all of the fixes introduced in 69d37d5 that set slp->slptr to null have been improved with the fix in f24040e.

The isaname, isaletter, isadigit, isexp and ismeta macros don't check if c is a negative value before accessing sh_lexstates. This can result in ASan crashing because of a buffer overflow in quoting2.sh when running in a multibyte locale: test quoting2(C.UTF-8) begins at 2022-09-23+14:03:12 ================================================================= ==262224==ERROR: AddressSanitizer: global-buffer-overflow on address 0x557b201a451f at pc 0x557b1fe5e6fc bp 0x7fffcf1ac700 sp 0x7fffcf1ac6f8 READ of size 1 at 0x557b201a451f thread T0 #0 0x557b1fe5e6fb in sh_fmtq /home/johno/GitRepos/KornShell/ksh/src/cmd/ksh93/sh/string.c:341:5 ksh93#1 0x557b1fe6098c in sh_fmtqf /home/johno/GitRepos/KornShell/ksh/src/cmd/ksh93/sh/string.c:473:10 ksh93#2 0x557b1ff08dc0 in extend /home/johno/GitRepos/KornShell/ksh/src/cmd/ksh93/bltins/print.c:998:14 ksh93#3 0x557b2008a56c in sfvprintf /home/johno/GitRepos/KornShell/ksh/src/lib/libast/sfio/sfvprintf.c:531:8 ksh93#4 0x557b2005b7f7 in sfprintf /home/johno/GitRepos/KornShell/ksh/src/lib/libast/sfio/sfprintf.c:31:7 ksh93#5 0x557b1ff04272 in b_print /home/johno/GitRepos/KornShell/ksh/src/cmd/ksh93/bltins/print.c:343:4 ksh93#6 0x557b1ff04ebf in b_printf /home/johno/GitRepos/KornShell/ksh/src/cmd/ksh93/bltins/print.c:148:9 ksh93#7 0x557b1fe8d9a7 in sh_exec /home/johno/GitRepos/KornShell/ksh/src/cmd/ksh93/sh/xec.c:1261:21 ksh93#8 0x557b1fe7a7cf in sh_subshell /home/johno/GitRepos/KornShell/ksh/src/cmd/ksh93/sh/subshell.c:652:4 ksh93#9 0x557b1fdedc0d in comsubst /home/johno/GitRepos/KornShell/ksh/src/cmd/ksh93/sh/macro.c:2207:9 ksh93#10 0x557b1fdefc79 in varsub /home/johno/GitRepos/KornShell/ksh/src/cmd/ksh93/sh/macro.c:1181:3 ksh93#11 0x557b1fde3bef in copyto /home/johno/GitRepos/KornShell/ksh/src/cmd/ksh93/sh/macro.c:620:21 ksh93#12 0x557b1fde0b07 in sh_mactrim /home/johno/GitRepos/KornShell/ksh/src/cmd/ksh93/sh/macro.c:169:2 ksh93#13 0x557b1fe05ab6 in nv_setlist /home/johno/GitRepos/KornShell/ksh/src/cmd/ksh93/sh/name.c:280:9 ksh93#14 0x557b1fe8a7e8 in sh_exec /home/johno/GitRepos/KornShell/ksh/src/cmd/ksh93/sh/xec.c:1051:7 ksh93#15 0x557b1fe95b85 in sh_exec /home/johno/GitRepos/KornShell/ksh/src/cmd/ksh93/sh/xec.c:1940:5 ksh93#16 0x557b1fe99ea6 in sh_exec /home/johno/GitRepos/KornShell/ksh/src/cmd/ksh93/sh/xec.c:2271:10 ksh93#17 0x557b1fd23b04 in exfile /home/johno/GitRepos/KornShell/ksh/src/cmd/ksh93/sh/main.c:604:4 ksh93#18 0x557b1fd1fe10 in sh_main /home/johno/GitRepos/KornShell/ksh/src/cmd/ksh93/sh/main.c:369:2 ksh93#19 0x557b1fd1d585 in main /home/johno/GitRepos/KornShell/ksh/src/cmd/ksh93/sh/pmain.c:41:9 ksh93#20 0x7f55d5b5028f (/usr/lib/libc.so.6+0x2328f) (BuildId: 26c81e7e05ebaf40bac3523b7d76be0cd71fad82) ksh93#21 0x7f55d5b50349 in __libc_start_main (/usr/lib/libc.so.6+0x23349) (BuildId: 26c81e7e05ebaf40bac3523b7d76be0cd71fad82) ksh93#22 0x557b1fc158d4 in _start /build/glibc/src/glibc/csu/../sysdeps/x86_64/start.S:115 src/cmd/ksh93/include/lexstates.h: - Check if c is negative before accessing sh_lexstates. Backported from ksh2020: att@a7013320. I'll note that later in ksh2020 these macros became functions: att@adc589de. I didn't backport that commit because it requires the C99 bool type to avoid compiler warnings.

When ksh executes a script without a #! path (note that the AT&T team had a real disliking for #! paths), ksh forks and goes through a quick reinitialisation procedure. This is much faster than invoking a fully new shell but should have the same effect if it all works well. Unfortunately it's not worked all that well so far. Even after recent improvements (see referenced commits) I've been finding corner case problems. FYI, running a script without #! basically goes like this: * in path_spawn(), execve() fails with ENOEXEC because the file is not a binary executable and does not start with #! * this triggers 'case ENOEXEC:' which: * forks ksh * calls exscript() * exscript() cleans up & calls siglongjmp(*sh.jmplist,SH_JMPSCRIPT) * SH_JMPSCRIPT is the highest longjmp value, so *all* the previous sigsetjmp/sh_pushcontext calls are unwinded in reverse order, triggering all sorts of cleanup, state restoration, removal of local scopes, etc. * eventually, this lands us at the top sigsetjmp in sh_main() * sh_main() calls sh_reinit(), then resumes as if the shell had just been started This commit makes the following interrelated changes for the correct functioning of this procedure: 1. exscript() now exports the environment into a dedicated Stk_t buffer and sets environ[] to that. 2. Instead of re-using existing variables, sh_reinit() deletes everything and reinits all name-value trees from scratch, then re-imports the environment from environ[]. 3. Variable values that were imported from the environment are no longer treated specially with an NV_IMPORT attribute and the np->nvenv pointer to their value in environ[], fixing at least one crash.[*1] Details of the changes follow: src/cmd/ksh93/sh/path.c: - exscript(): Generate a new environ[] by activating a dedicated AST stack that will not be overwritten before calling sh_envgen(). This will allow sh_reinit() to delete all variables and then reimport the environment. The exporting must be done here, before siglongjmp, otherwise locally scoped exported variables won't be included (siglongjmp with SH_JMPSCRIPT triggers cleanup of all scopes). src/cmd/ksh93/sh/init.c: - sh_reinit(): Largely rewritten as follows. - Reset shell options first. This has the beneficial side effect of unsetting SH_RESTRICTED which interferes with unsetting certain variables, like PATH. - Remove workarounds for FPATH, SHLVL and tilde expansion disciplines; these will not be needed now. - Properly unset and delete all functions and built-ins. Since we now unset a function before deleting it, this should now free up their memory. (See nvdisc.c below for a change allowing removal of special built-ins.) - Properly unset all variables (which includes any associated discipline functions). Incorporate here the needed logic from sh_envnolocal() in name.c; most of it is unneeded (that function was previously used to cleanup local variables but has not been used for that for decades). So sh_envnolocal() is now unused. - Delete variables in a separate pass after unsetting variables and unsetting and deleting functions; this avoids use-after- free problems as well as possible "no parent" problems with namespace variables (e.g., .rc.status in our new kshrc.sh). - After all that, close and free up all function, alias, tracked alias, type and variable trees. - Free the contiguous built-in node space and the Init_t init context (with all the special variable discipline pointers). - Call nv_init (previously only called from sh_init) to reinitialise all of the above name-value stuff from scratch. It's the only way to be sure. - Re-import the environment as stored by exscript() above. - env_init(): - Per item 3 above and footnote 1 below, no longer set NV_IMPORT attribute and no longer point np->nvenv to the item in environ. - POSIX says, for 'environ': "Any application that directly modifies the pointers to which the environ variable points has undefined behavior."[*2] Yet, env_init() is indeed juggling the environ[] pointers to deal with variables that cannot be imported because their names are invalid (because they still need to be saved to be passed on to child processes). Replace the current approach with one where those env vars get allocated on the heap, pointed to by sh.save_env and counted by sh.save_env_n (renamed from sh.nenv). This only needs to be done once as ksh cannot use or change these variables. src/cmd/ksh93/sh/name.c: - sh_envgen(): Update to match env_init() change above. - pushnam() (called by sh_envgen()): Remove NV_IMPORT attribute check as per above and never get the value from the nvenv pointer -- simply always use nv_getval(). As of this change, the NV_IMPORT attribute is unused. The next commit will remove it and do related cleanups. - staknam(): is only called if value!=NULL, so remove that 'if'. - sh_envnolocal(): Removed. src/cmd/ksh93/sh/nvdisc.c: - assign(): Remove a check for the SH_INIT state bit that avoids freeing functions during sh_reinit(). This works fine now. - sh_addbuiltin(): Allow sh_reinit() to delete special builtins by checking for the SH_INIT state bit before throwing an error. src/cmd/ksh93/sh/nvtree.c: - outval(): Add a workaround for a use-after-free, introduced by the changes above, that occurred in the types.sh tests for #!-less scripts (types.sh:675-722). The use-after-free occurred here (abridged ASan trace follows; line numbers are current as of this commit): ==30849==ERROR: AddressSanitizer: heap-use-after-free [...] #0 in dttree dttree.c:393 #1 in sh_reinit init.c:1637 #2 in sh_main main.c:136 [...] The pointer was freed in the same loop via nv_delete() in outval: #0 in wrap_free+0x98 (libclang_rt.asan_osx_dynamic.dylib:[...]) #1 in nv_delete name.c:1318 #2 in outval nvtree.c:731 #3 in genvalue nvtree.c:905 #4 in walk_tree nvtree.c:1042 #5 in put_tree nvtree.c:1108 #6 in nv_putv nvdisc.c:144 #7 in _nv_unset name.c:2437 #8 in sh_reinit init.c:1645 #9 in sh_main main.c:136 [...] So, what happened was that the nv_delete() call on name.c:1318 (eventually resulting from the _nv_unset call on init.c:1645) freed the node pointed to by np, so that the next loop iteration crashed on line 1637 as the dtnext() macro now gets a freed np. Now, why on earth should _nv_unset() *ever* indirectly call nv_delete()? That's a question for another day; I suspect it may be a bug, or it may be needed for compound variables for some reason. For now, I'm adding a workaround: simply avoid calling nv_delete() if the SH_INIT state bit is on, indicating sh_reinit() is in the call stack. This allows the variables unset loop in sh_reinit() to continue without crashing. sh_reinit() handles deletion later anyway. src/cmd/ksh93/sh/main.c: - sh_main(): remove zeroing of sh.fun_depth and sh.dot_depth; these are known to be 0, coming from either sh_init() or sh_reinit(). ________ [*1] This NV_IMPORT/nvenv usage is a redundant holdout from ancient ksh code; the imported value is easily available as a normal shell variable value via nv_getval(). Plus, the nvenv pointer is overloaded with too many other purposes: so far I've discovered it's used for pointers to subarrays of arrays (multidimentional arrays), compound variables, builtins, and other things. This mess caused at least one crash in set_instance() (xec.c) due to incorrectly using that nvenv pointer. The current kshrc script triggers this. Reproducer: $ export PS1 $ bin/package use «0»26:…/src/ksh93/ksh[dev] $ typeset +x PS1 ...and crash. That is now fixed. [*2] https://pubs.opengroup.org/onlinepubs/9699919799/functions/environ.html

The referenced commit left one test unexecuted because it crashes. Minimal reproducer: typeset -a arr=((a b c) 1) got=$( typeset -a arr=( ( ((a b c)1))) ) The crash occurs when the array is redefined in a subshell. Here are abridged ASan stack traces for the crash, for the use after free, and for when it was freed: ================================================================= ==73147==ERROR: AddressSanitizer: heap-use-after-free [snippage] READ of size 8 at 0x000107403eb0 thread T0 #0 0x104fded40 in nv_search nvdisc.c:1007 #1 0x104fbeb1c in nv_create name.c:860 #2 0x104fb8b9c in nv_open name.c:1440 #3 0x104fb1edc in nv_setlist name.c:309 #4 0x104fb4a30 in nv_setlist name.c:475 #5 0x105055b58 in sh_exec xec.c:1079 #6 0x105045cd4 in sh_subshell subshell.c:654 #7 0x104f92c1c in comsubst macro.c:2266 [snippage] 0x000107403eb0 is located 0 bytes inside of 80-byte region [snippage] freed by thread T0 here: #0 0x105c5ade4 in wrap_free+0x98 (libclang_rt.asan_osx_dynamic.dylib:arm64e+0x3ede4) #1 0x105261da0 in dtclose dtclose.c:52 #2 0x104f178cc in array_putval array.c:671 #3 0x104fd7f4c in nv_putv nvdisc.c:144 #4 0x104fbc5f0 in _nv_unset name.c:2435 #5 0x104fb3250 in nv_setlist name.c:364 #6 0x105055b58 in sh_exec xec.c:1079 #7 0x105045cd4 in sh_subshell subshell.c:654 #8 0x104f92c1c in comsubst macro.c:2266 [snippage] So the crash is caused because array_putval (array.c:671) calls dtclose, freeing ap->table, which is then reused after a recursive nv_setlist call via nv_open() -> nv_create() -> nv_search(). This only happens whwn we're in a virtual subshell. src/cmd/ksh93/sh/array.c: - array_putval(): When redefining an array in a virtual subshell, do not free the old ap->table; it will be needed by the parent shell environment.

JohnoKing force-pushed the fix-special-vars branch 2 times, most recently from 29ff473 to 6685cac Compare June 13, 2020 13:15

McDutchie reviewed Jun 13, 2020

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JohnoKing force-pushed the fix-special-vars branch from 6685cac to 0f52247 Compare June 13, 2020 19:52

JohnoKing force-pushed the fix-special-vars branch from 0f52247 to 7b994b6 Compare June 13, 2020 19:57

McDutchie merged commit a739115 into ksh93:master Jun 13, 2020

JohnoKing deleted the fix-special-vars branch June 18, 2020 02:45

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Implement a better fix for unsetting special env vars #7

Implement a better fix for unsetting special env vars #7

JohnoKing commented Jun 13, 2020 •

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	if(nv_isattr(np,NV_NOFREE))
	nv_onattr(mp,NV_IDENT);
	nv_clone(np,mp,(add?(nv_isnull(np)?0:NV_NOFREE)\|NV_ARRAY:NV_MOVE));
	shp->subshell = save;
	return(np);

	if(flags&NV_MOVE)
	{
	if(nv_isattr(np,NV_INTEGER))
	mp->nvalue.ip = np->nvalue.ip;
	np->nvfun = 0;

Implement a better fix for unsetting special env vars #7

Implement a better fix for unsetting special env vars #7

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