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daemon/remote.c:965:38: warning: ‘__builtin___snprintf_chk’ output may be truncated before the last format character #169

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noloader opened this issue Feb 27, 2020 · 2 comments

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@noloader
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noloader commented Feb 27, 2020

Hi Everyone,

I'm working from master and using instrumented builds. Building on Ubuntu 18.04 with UBsan:

libtool: compile:  gcc -I. -DSRCDIR=. -DNDEBUG -g2 -O3 -fsanitize=undefined -fno-sanitize-recover -pthread -c daemon/remote.c  -fPIC -DPIC -o .libs/remote.o
...
daemon/remote.c: In function ‘do_stats’:
daemon/remote.c:965:38: warning: ‘__builtin___snprintf_chk’ output may be truncated before the last format character [-Wformat-truncation=]
    snprintf(nm, sizeof(nm), "OPCODE%d", i);
                                      ^
In file included from /usr/include/stdio.h:862:0,
                 from ./config.h:1022,
                 from daemon/remote.c:45:
/usr/include/x86_64-linux-gnu/bits/stdio2.h:64:10: note: ‘__builtin___snprintf_chk’ output between 8 and 17 bytes into a destination of size 16
   return __builtin___snprintf_chk (__s, __n, __USE_FORTIFY_LEVEL - 1,
          ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
        __bos (__s), __fmt, __va_arg_pack ());
        ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

You can setup the test rig by exporting CFLAGS with UBsan enabled:

$ git clone https://github.com/NLnetLabs/unbound.git
$ cd unbound
$ export CFLAGS="-DNDEBUG -g2 -O3 -fsanitize=undefined -fno-sanitize-recover"
$ ./make-master.sh
...
$ make test
...
@wcawijngaards
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wcawijngaards commented Feb 27, 2020

Thanks, I guess the buffer increase in the commit 348e246 should do the trick. Nice that it tests for potential buffer exceeded for the fixed strings. In practice this statistics counter probably does not get to maxint, but it is good to fix anyway.

@noloader
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noloader commented Feb 27, 2020

Thanks @wcawijngaards.

Yeah, this is one of those annoying squawks, like a little dog that nips at your ankles.

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