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    Subject[PATCH 4.19 078/139] btrfs: relocation: set trans to be NULL after ending transaction
    Date
    4.19-stable review patch.  If anyone has any objections, please let me know.

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

    From: Pan Bian <bianpan2016@163.com>

    commit 42a657f57628402c73237547f0134e083e2f6764 upstream.

    The function relocate_block_group calls btrfs_end_transaction to release
    trans when update_backref_cache returns 1, and then continues the loop
    body. If btrfs_block_rsv_refill fails this time, it will jump out the
    loop and the freed trans will be accessed. This may result in a
    use-after-free bug. The patch assigns NULL to trans after trans is
    released so that it will not be accessed.

    Fixes: 0647bf564f1 ("Btrfs: improve forever loop when doing balance relocation")
    CC: stable@vger.kernel.org # 4.4+
    Reviewed-by: Qu Wenruo <wqu@suse.com>
    Signed-off-by: Pan Bian <bianpan2016@163.com>
    Reviewed-by: David Sterba <dsterba@suse.com>
    Signed-off-by: David Sterba <dsterba@suse.com>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

    ---
    fs/btrfs/relocation.c | 1 +
    1 file changed, 1 insertion(+)

    --- a/fs/btrfs/relocation.c
    +++ b/fs/btrfs/relocation.c
    @@ -3963,6 +3963,7 @@ static noinline_for_stack int relocate_b
    restart:
    if (update_backref_cache(trans, &rc->backref_cache)) {
    btrfs_end_transaction(trans);
    + trans = NULL;
    continue;
    }


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