[Bug libc/18093] Corrupted aux-cache causes ldconfig to segfault

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https://sourceware.org/bugzilla/show_bug.cgi?id=18093

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https://sourceware.org/git/gitweb.cgi?p=glibc.git;h=6a1cf708dd5681b517744d6d4fac02e4e4a0aa2e

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.

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Summary of changes:
 ChangeLog   |    6 ++++++
 NEWS        |    2 +-
 elf/cache.c |    4 +++-
 3 files changed, 10 insertions(+), 2 deletions(-)

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