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    SubjectRe: [PATCH] fs: Initialize tmp.b_page in generic_block_bmap()
    On Wed, Jan 18, 2017 at 5:32 PM, Theodore Ts'o <tytso@mit.edu> wrote:
    > On Thu, Dec 22, 2016 at 01:30:15PM +0100, Alexander Potapenko wrote:
    >> KMSAN (KernelMemorySanitizer, a new error detection tool) reports use of
    >> uninitialized memory in ext4_update_bh_state():
    >>
    >> ==================================================================
    >> BUG: KMSAN: use of unitialized memory
    >> CPU: 3 PID: 1 Comm: swapper/0 Tainted: G B 4.8.0-rc6+ #597
    >> Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Bochs
    >> 01/01/2011
    >> 0000000000000282 ffff88003cc96f68 ffffffff81f30856 0000003000000008
    >> ffff88003cc96f78 0000000000000096 ffffffff8169742a ffff88003cc96ff8
    >> ffffffff812fc1fc 0000000000000008 ffff88003a1980e8 0000000100000000
    >> Call Trace:
    >> [< inline >] __dump_stack lib/dump_stack.c:15
    >> [<ffffffff81f30856>] dump_stack+0xa6/0xc0 lib/dump_stack.c:51
    >> [<ffffffff812fc1fc>] kmsan_report+0x1ec/0x300 mm/kmsan/kmsan.c:?
    >> [<ffffffff812fc33b>] __msan_warning+0x2b/0x40 ??:?
    >> [< inline >] ext4_update_bh_state fs/ext4/inode.c:727
    >> [<ffffffff8169742a>] _ext4_get_block+0x6ca/0x8a0 fs/ext4/inode.c:759
    >> [<ffffffff81696d4c>] ext4_get_block+0x8c/0xa0 fs/ext4/inode.c:769
    >> [<ffffffff814a2d36>] generic_block_bmap+0x246/0x2b0 fs/buffer.c:2991
    >> [<ffffffff816ca30e>] ext4_bmap+0x5ee/0x660 fs/ext4/inode.c:3177
    >> ...
    >> origin description: ----tmp@generic_block_bmap
    >> ==================================================================
    >>
    >> (the line numbers are relative to 4.8-rc6, but the bug persists
    >> upstream)
    >>
    >> The local |tmp| is created in generic_block_bmap() and then passed into
    >> ext4_bmap() => ext4_get_block() => _ext4_get_block() =>
    >> ext4_update_bh_state(). Along the way tmp.b_page is never initialized
    >> before ext4_update_bh_state() checks its value.
    >>
    >> Signed-off-by: Alexander Potapenko <glider@google.com>
    >
    > This is a one-line fix to fs/buffer.c; but I've investigated, and
    > since it only affects ext4, and no one else has responded, I'll take
    > the change through the ext4 git tree.
    >
    > Thanks!!
    >
    > - Ted

    Hi Ted,

    any updates on this patch?
    Looks like it hasn't been landed yet.

    Alex

    --
    Alexander Potapenko
    Software Engineer

    Google Germany GmbH
    Erika-Mann-Straße, 33
    80636 München

    Geschäftsführer: Matthew Scott Sucherman, Paul Terence Manicle
    Registergericht und -nummer: Hamburg, HRB 86891
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