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sd-bus: fix memstream buffer extraction

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I'm getting the following error under valgrind:

==305970== Invalid free() / delete / delete[] / realloc()
==305970==    at 0x483E9F1: free (vg_replace_malloc.c:538)
==305970==    by 0x4012CD: mfree (alloc-util.h:48)
==305970==    by 0x4012EF: freep (alloc-util.h:83)
==305970==    by 0x4017F4: LLVMFuzzerTestOneInput (fuzz-bus-match.c:58)
==305970==    by 0x401A58: main (fuzz-main.c:39)
==305970==  Address 0x59972f0 is 0 bytes inside a block of size 8,192 free'd
==305970==    at 0x483FCE4: realloc (vg_replace_malloc.c:834)
==305970==    by 0x4C986F7: _IO_mem_finish (in /usr/lib64/libc-2.33.so)
==305970==    by 0x4C8F5E0: fclose@@GLIBC_2.2.5 (in /usr/lib64/libc-2.33.so)
==305970==    by 0x49D2CDB: fclose_nointr (fd-util.c:108)
==305970==    by 0x49D2D3D: safe_fclose (fd-util.c:124)
==305970==    by 0x4A4BCCC: fclosep (fd-util.h:41)
==305970==    by 0x4A4E00F: bus_match_to_string (bus-match.c:859)
==305970==    by 0x4016C2: LLVMFuzzerTestOneInput (fuzz-bus-match.c:58)
==305970==    by 0x401A58: main (fuzz-main.c:39)
==305970==  Block was alloc'd at
==305970==    at 0x483FAE5: calloc (vg_replace_malloc.c:760)
==305970==    by 0x4C98787: open_memstream (in /usr/lib64/libc-2.33.so)
==305970==    by 0x49D56D6: open_memstream_unlocked (fileio.c:97)
==305970==    by 0x4A4DEC5: bus_match_to_string (bus-match.c:859)
==305970==    by 0x4016C2: LLVMFuzzerTestOneInput (fuzz-bus-match.c:58)
==305970==    by 0x401A58: main (fuzz-main.c:39)
==305970==

So the fclose() which is called from _cleanup_fclose_ clearly reallocates the
buffer (maybe to save memory?). open_memstream(3) says:

  The locations referred to by these pointers are updated each time the
  stream is flushed (fflush(3)) and  when the stream is closed (fclose(3)).

This seems to mean that we should close the stream first before grabbing the
buffer pointer.
This commit is contained in:
Zbigniew Jędrzejewski-Szmek 2021-03-04 21:19:02 +01:00
parent 49ba1522fc
commit 5963e6f43c
1 changed files with 4 additions and 4 deletions
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8
src/libsystemd/sd-bus/bus-match.c
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@ -846,7 +846,7 @@ fail:
}
char *bus_match_to_string(struct bus_match_component *components, unsigned n_components) {
char *buffer = NULL;
_cleanup_free_ char *buffer = NULL;
size_t size = 0;
int r;
@ -855,7 +855,7 @@ char *bus_match_to_string(struct bus_match_component *components, unsigned n_com
assert(components);
_cleanup_fclose_ FILE *f = open_memstream_unlocked(&buffer, &size);
FILE *f = open_memstream_unlocked(&buffer, &size);
if (!f)
return NULL;
@ -878,10 +878,10 @@ char *bus_match_to_string(struct bus_match_component *components, unsigned n_com
}
r = fflush_and_check(f);
safe_fclose(f);
if (r < 0)
return NULL;
return buffer;
return TAKE_PTR(buffer);
}
int bus_match_add(