fix crash caused by free of uninitialized pointer

[maep--]

No description provided.

[richardgv]

Yes. that's possible, and thanks for the patch.

I looked into libX11-1.6.2's source code. Seemingly it would happen when X fails to allocate memory or _XlcOpenConverter() fails -- sounds like very rare cases. Could you please provide us some information about how you triggered the issue?

[maep--]

I started compton without any extra flags and no config file. It crashed on the first call to make_text_prop function().

card: radeon HD 7850 using open source radeon drivers.
xorg: 1.16.0
libx11: 1.6.2
kernel: 3.15.8-1-ARCH

crash message before my fix (revision 4f9050f):

*** Error in `./compton': free(): invalid pointer: 0x00007f1c6a720380 ***
======= Backtrace: =========
/usr/lib/libc.so.6(+0x73f8e)[0x7f1c6a3ecf8e]
/usr/lib/libc.so.6(+0x7988e)[0x7f1c6a3f288e]
/usr/lib/libc.so.6(+0x7a04b)[0x7f1c6a3f304b]
/usr/lib/libX11.so.6(XFree+0x9)[0x7f1c6b1ded79]
./compton[0x40781d]
./compton[0x408c8b]
./compton[0x408cd0]
./compton[0x413e8f]
./compton[0x4193b7]
./compton[0x41a39c]
/usr/lib/libc.so.6(__libc_start_main+0xf0)[0x7f1c6a399000]
./compton[0x406a29]

compiled with -fsanitize=address I a decent stacktrace:

ASAN:SIGSEGV
=================================================================
==3174==ERROR: AddressSanitizer: SEGV on unknown address 0x000000000000 (pc 0x7f6f6eb2089d sp 0x7fff330db580 bp 0xbebebebebebebebe T0)
    #0 0x7f6f6eb2089c (/usr/lib/libasan.so.1+0x1e89c)
    #1 0x7f6f6eb59894 in __interceptor_free (/usr/lib/libasan.so.1+0x57894)
    #2 0x7f6f6d810d78 in XFree (/usr/lib/libX11.so.6+0x44d78)
    #3 0x408fa2 in cxfree src/common.h:1834
    #4 0x40c6fa in make_text_prop src/compton.h:357
    #5 0x40c73f in wid_set_text_prop src/compton.h:371
    #6 0x42a52e in register_cm src/compton.c:4784
    #7 0x43823c in session_init src/compton.c:7248
    #8 0x43abd3 in main src/compton.c:7639
    #9 0x7f6f6c9cafff in __libc_start_main (/usr/lib/libc.so.6+0x1ffff)
    #10 0x407048 (/home/maep/code/compton/compton+0x407048)

AddressSanitizer can not provide additional info.
SUMMARY: AddressSanitizer: SEGV ??:0 ??
==3174==ABORTING

I hope this helps. I don't know much about X11 but I'd be glad to do a bit of testing / debugging as far as my time allows.

edit: after the fix git this message

wid_set_text_prop("git-v0.1_beta2-44-g82242f5-2014-08-07"): Failed to make text property.
register_cm(): Failed to set COMPTON_VERSION.

[richardgv]

Sorry for the very late reply. I forgot about the issue.

It might have something to do with locale? I'm not able to reproduce the issue by trying different combinations of locales of compton and X here. Anyway, it isn't fatal. Thanks for the info!

[maep--]

My locale is en_DK.UTF-8.