[Bug malloc/17730] thread-local storage is sometimes improperly free()'d after being __libc_memalign()'d

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https://sourceware.org/bugzilla/show_bug.cgi?id=17730

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https://sourceware.org/git/gitweb.cgi?p=glibc.git;h=6c444ad6e953dbdf9c7be065308a0a7779d32bb2

commit 6c444ad6e953dbdf9c7be065308a0a7779d32bb2
Author: Florian Weimer <fweimer@redhat.com>
Date:   Wed Aug 3 16:16:57 2016 +0200

    elf: Do not use memalign for TCB/TLS blocks allocation [BZ #17730]

    Instead, call malloc and explicitly align the pointer.

    There is no external location to store the original (unaligned)
    pointer, and this commit increases the allocation size to store
    the pointer at a fixed location relative to the TCB pointer.

    The manual alignment means that some space goes unused which
    was previously made available for subsequent allocations.
    However, in the TLS_DTV_AT_TP case, the manual alignment code
    avoids aligning the pre-TCB to the TLS block alignment.  (Even
    while using memalign, the allocation had some unused padding
    in front.)

    This concludes the removal of memalign calls from the TLS code,
    and the new tst-tls3-malloc test verifies that only core malloc
    routines are used.

https://sourceware.org/git/gitweb.cgi?p=glibc.git;h=a2ff21f825adb8821eeb6145197fa8b9a8a60a58

commit a2ff21f825adb8821eeb6145197fa8b9a8a60a58
Author: Florian Weimer <fweimer@redhat.com>
Date:   Wed Aug 3 16:15:38 2016 +0200

    elf: Avoid using memalign for TLS allocations [BZ #17730]

    Instead of a flag which indicates the pointer can be freed, dtv_t
    now includes the pointer which should be freed.  Due to padding,
    the size of dtv_t does not increase.

    To avoid using memalign, the new allocate_dtv_entry function
    allocates a sufficiently large buffer so that a sub-buffer
    can be found in it which starts with an aligned pointer.  Both
    the aligned and original pointers are kept, the latter for calling
    free later.

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

Summary of changes:
 ChangeLog                |   37 ++++++++++
 csu/libc-tls.c           |    2 +-
 elf/dl-tls.c             |  164 ++++++++++++++++++++++++++-----------------
 nptl/Makefile            |    8 ++-
 nptl/allocatestack.c     |    4 +-
 nptl/tst-tls3-malloc.c   |  176 ++++++++++++++++++++++++++++++++++++++++++++++
 sysdeps/generic/dl-dtv.h |   12 ++--
 7 files changed, 327 insertions(+), 76 deletions(-)
 create mode 100644 nptl/tst-tls3-malloc.c

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