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    Subject[PATCH 3.16 097/305] Btrfs: fix null pointer dereference on compressed write path error
    3.16.63-rc1 review patch.  If anyone has any objections, please let me know.

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

    From: Filipe Manana <fdmanana@suse.com>

    commit 3527a018c00e5dbada2f9d7ed5576437b6dd5cfb upstream.

    At inode.c:compress_file_range(), under the "free_pages_out" label, we can
    end up dereferencing the "pages" pointer when it has a NULL value. This
    case happens when "start" has a value of 0 and we fail to allocate memory
    for the "pages" pointer. When that happens we jump to the "cont" label and
    then enter the "if (start == 0)" branch where we immediately call the
    cow_file_range_inline() function. If that function returns 0 (success
    creating an inline extent) or an error (like -ENOMEM for example) we jump
    to the "free_pages_out" label and then access "pages[i]" leading to a NULL
    pointer dereference, since "nr_pages" has a value greater than zero at
    that point.

    Fix this by setting "nr_pages" to 0 when we fail to allocate memory for
    the "pages" pointer.

    Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=201119
    Fixes: 771ed689d2cd ("Btrfs: Optimize compressed writeback and reads")
    Reviewed-by: Liu Bo <bo.liu@linux.alibaba.com>
    Signed-off-by: Filipe Manana <fdmanana@suse.com>
    Reviewed-by: David Sterba <dsterba@suse.com>
    Signed-off-by: David Sterba <dsterba@suse.com>
    Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
    ---
    fs/btrfs/inode.c | 1 +
    1 file changed, 1 insertion(+)

    --- a/fs/btrfs/inode.c
    +++ b/fs/btrfs/inode.c
    @@ -452,6 +452,7 @@ again:
    pages = kzalloc(sizeof(struct page *) * nr_pages, GFP_NOFS);
    if (!pages) {
    /* just bail out to the uncompressed code */
    + nr_pages = 0;
    goto cont;
    }

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