[Bug nscd/16453] nscd segfaults with a large number of members in a netgroup

[cvs-commit at gcc dot gnu.org]

http://sourceware.org/bugzilla/show_bug.cgi?id=16453

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- Log -----------------------------------------------------------------
https://sourceware.org/git/gitweb.cgi?p=glibc.git;h=5d29ccce66cc903fd9aa6e8f74c6be4dbc03d1f5

commit 5d29ccce66cc903fd9aa6e8f74c6be4dbc03d1f5
Author: Siddhesh Poyarekar <siddhesh@redhat.com>
Date:   Thu Jan 16 10:19:18 2014 +0530

    Mention addition of multiple precision fallback libm probes in NEWS

https://sourceware.org/git/gitweb.cgi?p=glibc.git;h=980cb5180e1b71224a57ca52b995c959b7148c09

commit 980cb5180e1b71224a57ca52b995c959b7148c09
Author: Siddhesh Poyarekar <siddhesh@redhat.com>
Date:   Thu Jan 16 10:20:22 2014 +0530

    Don't use alloca in addgetnetgrentX (BZ #16453)

    addgetnetgrentX has a buffer which is grown as per the needs of the
    requested size either by using alloca or by falling back to malloc if
    the size is larger than 1K.  There are two problems with the alloca
    bits: firstly, it doesn't really extend the buffer since it does not
    use the return value of the extend_alloca macro, which is the location
    of the reallocated buffer.  Due to this the buffer does not actually
    extend itself and hence a subsequent write may overwrite stuff on the
    stack.

    The second problem is more subtle - the buffer growth on the stack is
    discontinuous due to block scope local variables.  Combine that with
    the fact that unlike realloc, extend_alloca does not copy over old
    content and you have a situation where the buffer just has garbage in
    the space where it should have had data.

    This could have been fixed by adding code to copy over old data
    whenever we call extend_alloca, but it seems unnecessarily
    complicated.  This code is not exactly a performance hotspot (it's
    called when there is a cache miss, so factors like network lookup or
    file reads will dominate over memory allocation/reallocation), so this
    premature optimization is unnecessary.

    Thanks Brad Hubbard <bhubbard@redhat.com> for his help with debugging
    the problem.

-----------------------------------------------------------------------

Summary of changes:
 ChangeLog            |    5 +++++
 NEWS                 |    5 ++++-
 nscd/netgroupcache.c |   37 ++++++-------------------------------
 3 files changed, 15 insertions(+), 32 deletions(-)

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