I looked at ways the aux-cache could cause a segfault, and given the file is mmap'd and has data offsets in it that are used as pointers without being checked it is not hard to see how a corrupt file could cause a segfault. The following patch makes the segfaults I was able to think of and create go away.
I also have included an example corrupted aux-cache file
(aux-cache-corrupt-soname-offset) which has a bad offset that causes
a segfault.
There is another problem which I haven't solved but which is not a
segfault. If you somehow truncate the aux-cache file by a bit and run
the previous ldconfig without my patch, then you end up with a corrupted
aux-cache where some entries do not have soname's even though they should,
and that causes you to get messages like:
/sbin/ldconfig.real: /lib/i386-linux-gnu/ is not a symbolic link
/sbin/ldconfig.real: /usr/lib/i386-linux-gnu/ is not a symbolic link
/sbin/ldconfig.real: /lib64/ is not a symbolic link
/sbin/ldconfig.real: /usr/lib64/ is not a symbolic link
/sbin/ldconfig.real: /libx32/ is not a symbolic link
/sbin/ldconfig.real: /usr/libx32/ is not a symbolic link
/sbin/ldconfig.real: /usr/lib/ is not a symbolic link
/sbin/ldconfig.real: /usr/lib/i386-linux-gnu/i586/ is not a symbolic link
/sbin/ldconfig.real: /usr/lib/i386-linux-gnu/i686/cmov/ is not a symbolic link
Using ldconfig -i (and hence ignoring the corrupted aux-cache) makes
that problem go away. To solve it would of course mean you have to
not trust the cache which rather defeats the point of having the cache,
so I don't know if that is worth trying to solve. It does not cause a
segfault however.
Using ldconfig -p to show the cache at that point has entries that are
clearly wrong such as:
...
day (libc6, OS ABI: Linux 2.6.32) => /lib/i386-linux-gnu/day
__kernel_sigreturn (libc6,x32, OS ABI: Linux 3.4.0) =>
/libx32/__kernel_sigreturn
X_2.6 (libc6) => /usr/lib/i386-linux-gnu/X_2.6
LF (libc6) => /usr/lib/i386-linux-gnu/LF
(libc6) => /usr/lib/
(libc6, OS ABI: Linux 2.6.32) => /lib/i386-linux-gnu/
(libc6, OS ABI: Linux 2.6.32) => /usr/lib/i386-linux-gnu/
(libc6) => /lib/i386-linux-gnu/
(libc6) => /usr/lib/i386-linux-gnu/
(libc6) => /usr/lib/i386-linux-gnu/
(libc6) => /usr/lib/i386-linux-gnu/
(libc6) => /usr/lib/i386-linux-gnu/
(libc6, OS ABI: Linux 2.6.32) => /lib/i386-linux-gnu/
(libc6, OS ABI: Linux 2.6.32) => /usr/lib/i386-linux-gnu/
(libc6,x32, OS ABI: Linux 3.4.0) => /libx32/
(libc6,x32, OS ABI: Linux 3.4.0) => /usr/libx32/
(libc6,x86-64, OS ABI: Linux 2.6.32) => /lib64/
(libc6,x86-64, OS ABI: Linux 2.6.32) => /usr/lib64/
(libc6, hwcap: 0x0008000000008000) =>
/usr/lib/i386-linux-gnu/i686/cmov/
(libc6, hwcap: 0x0004000000000000) => /usr/lib/i386-linux-gnu/i586/
(libc6) => /lib/i386-linux-gnu/
(libc6) => /usr/lib/i386-linux-gnu/
(libc6) => /usr/lib/
� (libc6) => /lib/i386-linux-gnu/�
The file aux-cache-missing-sonames shows this corrupted state.
I hope the patch at least helps solve the worst part of the problem.
--
Len Sorensen
diff -ur --exclude debian --exclude build-tree glibc-2.19.ori/elf/cache.c glibc-2.19/elf/cache.c
--- glibc-2.19.ori/elf/cache.c 2015-02-25 16:24:59.000000000 +0000
+++ glibc-2.19/elf/cache.c 2015-02-25 17:42:18.000000000 +0000
@@ -699,7 +699,8 @@
if (aux_cache == MAP_FAILED
|| aux_cache_size < sizeof (struct aux_cache_file)
|| memcmp (aux_cache->magic, AUX_CACHEMAGIC, sizeof AUX_CACHEMAGIC - 1)
- || aux_cache->nlibs >= aux_cache_size)
+ || sizeof(struct aux_cache_file) + (aux_cache->nlibs - 1) * sizeof(struct aux_cache_file_entry) >= aux_cache_size
+ || aux_cache->nlibs * sizeof(struct aux_cache_file_entry) + aux_cache->libs[aux_cache->nlibs - 1].soname >= aux_cache_size)
{
close (fd);
init_aux_cache ();
@@ -712,12 +713,14 @@
const char *aux_cache_data
= (const char *) &aux_cache->libs[aux_cache->nlibs];
for (unsigned int i = 0; i < aux_cache->nlibs; ++i)
- insert_to_aux_cache (&aux_cache->libs[i].id,
- aux_cache->libs[i].flags,
- aux_cache->libs[i].osversion,
- aux_cache->libs[i].soname == 0
- ? NULL : aux_cache_data + aux_cache->libs[i].soname,
- 0);
+ /* Only use entries with sane offsets */
+ if (aux_cache->libs[i].soname < aux_cache_size)
+ insert_to_aux_cache (&aux_cache->libs[i].id,
+ aux_cache->libs[i].flags,
+ aux_cache->libs[i].osversion,
+ aux_cache->libs[i].soname == 0
+ ? NULL : aux_cache_data + aux_cache->libs[i].soname,
+ 0);
munmap (aux_cache, aux_cache_size);
close (fd);
aux-cache-corrupt-soname-offset
Description: Binary data
aux-cache-missing-sonames
Description: Binary data
