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    Subject[PATCH 4.4 090/268] md raid10: fix NULL deference in handle_write_completed()
    Date
    4.4-stable review patch.  If anyone has any objections, please let me know.

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

    From: Yufen Yu <yuyufen@huawei.com>

    [ Upstream commit 01a69cab01c184d3786af09e9339311123d63d22 ]

    In the case of 'recover', an r10bio with R10BIO_WriteError &
    R10BIO_IsRecover will be progressed by handle_write_completed().
    This function traverses all r10bio->devs[copies].
    If devs[m].repl_bio != NULL, it thinks conf->mirrors[dev].replacement
    is also not NULL. However, this is not always true.

    When there is an rdev of raid10 has replacement, then each r10bio
    ->devs[m].repl_bio != NULL in conf->r10buf_pool. However, in 'recover',
    even if corresponded replacement is NULL, it doesn't clear r10bio
    ->devs[m].repl_bio, resulting in replacement NULL deference.

    This bug was introduced when replacement support for raid10 was
    added in Linux 3.3.

    As NeilBrown suggested:
    Elsewhere the determination of "is this device part of the
    resync/recovery" is made by resting bio->bi_end_io.
    If this is end_sync_write, then we tried to write here.
    If it is NULL, then we didn't try to write.

    Fixes: 9ad1aefc8ae8 ("md/raid10: Handle replacement devices during resync.")
    Cc: stable (V3.3+)
    Suggested-by: NeilBrown <neilb@suse.com>
    Signed-off-by: Yufen Yu <yuyufen@huawei.com>
    Signed-off-by: Shaohua Li <sh.li@alibaba-inc.com>
    Signed-off-by: Sasha Levin <alexander.levin@microsoft.com>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
    ---
    drivers/md/raid10.c | 6 ++++--
    1 file changed, 4 insertions(+), 2 deletions(-)

    --- a/drivers/md/raid10.c
    +++ b/drivers/md/raid10.c
    @@ -2630,7 +2630,8 @@ static void handle_write_completed(struc
    for (m = 0; m < conf->copies; m++) {
    int dev = r10_bio->devs[m].devnum;
    rdev = conf->mirrors[dev].rdev;
    - if (r10_bio->devs[m].bio == NULL)
    + if (r10_bio->devs[m].bio == NULL ||
    + r10_bio->devs[m].bio->bi_end_io == NULL)
    continue;
    if (!r10_bio->devs[m].bio->bi_error) {
    rdev_clear_badblocks(
    @@ -2645,7 +2646,8 @@ static void handle_write_completed(struc
    md_error(conf->mddev, rdev);
    }
    rdev = conf->mirrors[dev].replacement;
    - if (r10_bio->devs[m].repl_bio == NULL)
    + if (r10_bio->devs[m].repl_bio == NULL ||
    + r10_bio->devs[m].repl_bio->bi_end_io == NULL)
    continue;

    if (!r10_bio->devs[m].repl_bio->bi_error) {

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