Re: [BUG] heap-use-after-free(read) pstrcmp() src/mystring.c

[Herbert Xu <herbert@gondor.apana.org.au>]

Aleksander Ushakov <aushakov@astralinux.ru> wrote:
> 
> I encountered a bug in Dash in commit fd725b7a75 and would like to 
> report it. The details are provided below.
> The target crashed when reading from memory after it has been freed.
> ==119==ERROR: AddressSanitizer: heap-use-after-free on address 
> 0x515000008f08 at pc 0x62b3e92a9f96 bp 0x7ffe2076bc00 sp 0x7ffe2076b3b0
> READ of size 1 at 0x515000008f08 thread T0
>     #0 0x62b3e92a9f95 in __interceptor_strcmp 
> ../../../../src/libsanitizer/sanitizer_common/sanitizer_common_interceptors.inc:466
>     #1 0x62b3e9353a34 in bsearch 
> /usr/include/x86_64-linux-gnu/bits/stdlib-bsearch.h:33
>     #2 0x62b3e9353a34 in findstring /upstream/dash/src/mystring.c:260
>     #3 0x62b3e935c140 in readtoken /upstream/dash/src/parser.c:737
>     #4 0x62b3e935ce76 in list /upstream/dash/src/parser.c:181
>     #5 0x62b3e936072e in readtoken1 /upstream/dash/src/parser.c:1587
>     #6 0x62b3e93693ff in parseheredoc /upstream/dash/src/parser.c:690
>     #7 0x62b3e93601d6 in readtoken1 /upstream/dash/src/parser.c:1597
>     #8 0x62b3e9369bc3 in xxreadtoken /upstream/dash/src/parser.c:843
>     #9 0x62b3e935bfb6 in readtoken /upstream/dash/src/parser.c:711
>     #10 0x62b3e935ce76 in list /upstream/dash/src/parser.c:181
>     #11 0x62b3e934a242 in cmdloop /upstream/dash/src/main.c:223
>     #12 0x62b3e922543c in main /upstream/dash/src/main.c:180
>     #13 0x7ab34e084249 in __libc_start_call_main 
> ../sysdeps/nptl/libc_start_call_main.h:58
>     #14 0x7ab34e084304 in __libc_start_main_impl ../csu/libc-start.c:360
>     #15 0x62b3e9226520 in _start (/upstream/dash/src/dash+0x1a520)
> 
> 0x515000008f08 is located 8 bytes inside of 512-byte region 
> [0x515000008f00,0x515000009100)
> freed by thread T0 here:
>     #0 0x62b3e92b9068 in __interceptor_free 
> ../../../../src/libsanitizer/asan/asan_malloc_linux.cpp:52
>     #1 0x62b3e934c8cd in popstackmark /upstream/dash/src/memalloc.c:187

Thanks for the report.  This is a manifestation of the fact that
the dash parser is not re-entrant.  Despite that, it gets called
recursively when a prompt needs to be generated during parsing.

Hence the crash.

Cheers,
-- 
Email: Herbert Xu <herbert@gondor.apana.org.au>
Home Page: http://gondor.apana.org.au/~herbert/
PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt