Subject: Re: bug#58042: 29.0.50; ASAN use-after-free in re_match_2_internal

From: Eli Zaretskii <[email-masked]>
Date: Sat, 24 Sep 2022 17:56:55 +0300

> From: Gerd Möllmann <[email-masked]>
> Date: Sat, 24 Sep 2022 16:17:20 +0200
> 
> Gerd Möllmann <[email-masked]> writes:
> 
> > ==79227==ERROR: AddressSanitizer: heap-use-after-free on address 0x00011f81e7d1 at pc 0x0001005825c4 bp 0x00016fdcf370 sp 0x00016fdcf368
> > READ of size 1 at 0x00011f81e7d1 thread T0
> >     #0 0x1005825c0 in re_match_2_internal regex-emacs.c:4352
> >     #1 0x10057e5cc in rpl_re_search_2 regex-emacs.c:3383
> >     #2 0x10057d1c4 in rpl_re_search regex-emacs.c:3177
> >     #3 0x10056115c in fast_string_match_internal search.c:492
> >     #4 0x1005045c0 in fast_string_match lisp.h:4818
> >     #5 0x100504018 in Ffind_file_name_handler fileio.c:324
> >     #6 0x1006dbe5c in openp lread.c:1911
> >     #7 0x1006d8844 in Fload lread.c:1302
> >     #8 0x1006e1af0 in save_match_data_load lread.c:1630
> >     #9 0x10064f8cc in load_with_autoload_queue eval.c:2269
> >     #10 0x10067d2f8 in Frequire fns.c:3274
> 
> Forget to copy the part where it is freed:
> 
> freed by thread T0 here:
>     #0 0x103332de4 in wrap_free+0x98 (libclang_rt.asan_osx_dynamic.dylib:arm64e+0x3ede4)
>     #1 0x100985e38 in rpl_free free.c:48
>     #2 0x1005b71a4 in lisp_free alloc.c:1038
>     #3 0x1005cbda4 in compact_small_strings alloc.c:2191
>     #4 0x1005c9f24 in sweep_strings alloc.c:2072
>     #5 0x1005bd028 in gc_sweep alloc.c:7397
>     #6 0x1005bb178 in garbage_collect alloc.c:6245
>     #7 0x1005ba694 in maybe_garbage_collect alloc.c:6090
>     #8 0x1006505ac in maybe_gc lisp.h:5624
>     #9 0x100648ffc in Ffuncall eval.c:2972
>     #10 0x10064bcd0 in internal_condition_case_n eval.c:1555
>     #11 0x1000cdc8c in safe__call xdisp.c:3026
>     #12 0x1000cdfc4 in safe__call1 xdisp.c:3062
>     #13 0x1001d6404 in prepare_menu_bars xdisp.c:13572
>     #14 0x1000f2340 in redisplay_internal xdisp.c:16523
>     #15 0x100108f34 in redisplay xdisp.c:16105
>     #16 0x10088fa84 in -[EmacsView layoutSublayersOfLayer:] nsterm.m:8662
>     #17 0x1900a9624 in CA::Layer::layout_if_needed(CA::Transaction*)+0x224 (QuartzCore:arm64e+0x20624)
>     #18 0x1901f661c in CA::Context::commit_transaction(CA::Transaction*, double, double*)+0x1c0 (QuartzCore:arm64e+0x16d61c)
>     #19 0x19008b4c8 in CA::Transaction::commit()+0x2bc (QuartzCore:arm64e+0x24c8)
>     #20 0x18bee1698 in __62+[CATransaction(NSCATransaction) NS_setFlushesWithDisplayLink]_block_invoke+0x12c (AppKit:arm64e+0x1ac698)
>     #21 0x18c646754 in ___NSRunLoopObserverCreateWithHandler_block_invoke+0x3c (AppKit:arm64e+0x911754)
>     #22 0x1892101a0 in __CFRUNLOOP_IS_CALLING_OUT_TO_AN_OBSERVER_CALLBACK_FUNCTION__+0x20 (CoreFoundation:arm64e+0x841a0)
>     #23 0x18920fff0 in __CFRunLoopDoObservers+0x24c (CoreFoundation:arm64e+0x83ff0)
>     #24 0x18920f524 in __CFRunLoopRun+0x300 (CoreFoundation:arm64e+0x83524)
>     #25 0x18920ea80 in CFRunLoopRunSpecific+0x254 (CoreFoundation:arm64e+0x82a80)
>     #26 0x191e4e334 in RunCurrentEventLoopInMode+0x120 (HIToolbox:arm64e+0x32334)
>     #27 0x191e4dfc0 in ReceiveNextEventCommon+0x140 (HIToolbox:arm64e+0x31fc0)
>     #28 0x191e4de64 in _BlockUntilNextEventMatchingListInModeWithFilter+0x44 (HIToolbox:arm64e+0x31e64)
>     #29 0x18bd76518 in _DPSNextEvent+0x358 (AppKit:arm64e+0x41518)

So it was freed by GC, which probably relocated string data or
something.  But I don't understand the relation between these two
backtraces: was the one that accessed a freed string called by the one
which triggered GC?  IOW, what is the relation between the call to
'require', which ended up calling re_match_2_internal, and the call to
prepare_menu_bars, which triggered GC?

re_search gets Lisp strings as its arguments, so unless GC was called
while the regexp search was in progress, I cannot understand how this
could happen.

Is there any way to know which argument of re_match_2_internal was
used to access the free'd heap?