[v2,BUG,18093] Fix ldconfig segmentation fault with corrupted cache
Commit Message
ldconfig is using an aux-cache to speed up the ld.so.cache update. It
is read by mmaping the file to a structure which contains data offsets
used as pointers. As they are not checked, it is not hard to get
ldconfig to segfault with a corrupted file. This happens for instance if
the file is truncated, which is common following a filesystem check
following a system crash.
This can be reproduced for example by truncating the file to roughly
half of it's size.
There is already some code in elf/cache.c (load_aux_cache) to check
for a corrupted aux cache, but it happens to be broken and not enough.
The test (aux_cache->nlibs >= aux_cache_size) compares the number of
libs entry with the cache size. It's a non sense, as it basically
assumes that each library entry is a 1 byte... Instead the patch below
computes the theoretical cache size using the headers and compares it
to the real size.
2015-03-11 Aurelien Jarno <aurelien@aurel32.net>
[BZ #18093]
* elf/cache.c (load_aux_cache): Regenerate the cache if it has the
wrong size.
Comments
On 03/11/2015 12:34 PM, Aurelien Jarno wrote:
> ldconfig is using an aux-cache to speed up the ld.so.cache update. It
> is read by mmaping the file to a structure which contains data offsets
> used as pointers. As they are not checked, it is not hard to get
> ldconfig to segfault with a corrupted file. This happens for instance if
> the file is truncated, which is common following a filesystem check
> following a system crash.
>
> This can be reproduced for example by truncating the file to roughly
> half of it's size.
>
> There is already some code in elf/cache.c (load_aux_cache) to check
> for a corrupted aux cache, but it happens to be broken and not enough.
> The test (aux_cache->nlibs >= aux_cache_size) compares the number of
> libs entry with the cache size. It's a non sense, as it basically
> assumes that each library entry is a 1 byte... Instead the patch below
> computes the theoretical cache size using the headers and compares it
> to the real size.
>
> 2015-03-11 Aurelien Jarno <aurelien@aurel32.net>
>
> [BZ #18093]
> * elf/cache.c (load_aux_cache): Regenerate the cache if it has the
> wrong size.
>
> diff --git a/elf/cache.c b/elf/cache.c
> index 1732268..bde7984 100644
> --- a/elf/cache.c
> +++ b/elf/cache.c
> @@ -698,7 +698,9 @@ load_aux_cache (const char *aux_cache_name)
> 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)
> + || aux_cache_size != (sizeof(struct aux_cache_file) +
> + aux_cache->nlibs * sizeof(struct aux_cache_file_entry) +
> + aux_cache->len_strings))
> {
> close (fd);
> init_aux_cache ();
>
I verified on Fedora Rawhide that without the patch
a truncated aux cache causes ldconfig to crash, and with the
new patch we re-initialize the cache.
I also verified with a debugger that it isn't just triggering
all the time resetting the cache.
Committed.
commit 6a1cf708dd5681b517744d6d4fac02e4e4a0aa2e
Author: Aurelien Jarno <aurelien@aurel32.net>
Date: Wed Mar 11 21:03:50 2015 -0400
Fix ldconfig segmentation fault with corrupted cache (Bug 18093).
ldconfig is using an aux-cache to speed up the ld.so.cache update. It
is read by mmaping the file to a structure which contains data offsets
used as pointers. As they are not checked, it is not hard to get
ldconfig to segfault with a corrupted file. This happens for instance if
the file is truncated, which is common following a filesystem check
following a system crash.
This can be reproduced for example by truncating the file to roughly
half of it's size.
There is already some code in elf/cache.c (load_aux_cache) to check
for a corrupted aux cache, but it happens to be broken and not enough.
The test (aux_cache->nlibs >= aux_cache_size) compares the number of
libs entry with the cache size. It's a non sense, as it basically
assumes that each library entry is a 1 byte... Instead this commit
computes the theoretical cache size using the headers and compares it
to the real size.
Cheers,
Carlos.
@@ -698,7 +698,9 @@ load_aux_cache (const char *aux_cache_name)
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)
+ || aux_cache_size != (sizeof(struct aux_cache_file) +
+ aux_cache->nlibs * sizeof(struct aux_cache_file_entry) +
+ aux_cache->len_strings))
{
close (fd);
init_aux_cache ();