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    Subject[066/140] md: raid10: Fix null pointer dereference in fix_read_error()
    2.6.33-stable review patch.  If anyone has any objections, please let us know.

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

    From: Prasanna S. Panchamukhi <prasanna.panchamukhi@riverbed.com>

    commit 0544a21db02c1d8883158fd6f323364f830a120a upstream.

    Such NULL pointer dereference can occur when the driver was fixing the
    read errors/bad blocks and the disk was physically removed
    causing a system crash. This patch check if the
    rcu_dereference() returns valid rdev before accessing it in fix_read_error().

    Signed-off-by: Prasanna S. Panchamukhi <prasanna.panchamukhi@riverbed.com>
    Signed-off-by: Rob Becker <rbecker@riverbed.com>
    Signed-off-by: NeilBrown <neilb@suse.de>
    Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

    ---
    drivers/md/raid10.c | 12 ++++++------
    1 file changed, 6 insertions(+), 6 deletions(-)

    --- a/drivers/md/raid10.c
    +++ b/drivers/md/raid10.c
    @@ -1486,14 +1486,14 @@ static void fix_read_error(conf_t *conf,
    int sectors = r10_bio->sectors;
    mdk_rdev_t*rdev;
    int max_read_errors = atomic_read(&mddev->max_corr_read_errors);
    + int d = r10_bio->devs[r10_bio->read_slot].devnum;

    rcu_read_lock();
    - {
    - int d = r10_bio->devs[r10_bio->read_slot].devnum;
    + rdev = rcu_dereference(conf->mirrors[d].rdev);
    + if (rdev) { /* If rdev is not NULL */
    char b[BDEVNAME_SIZE];
    int cur_read_error_count = 0;

    - rdev = rcu_dereference(conf->mirrors[d].rdev);
    bdevname(rdev->bdev, b);

    if (test_bit(Faulty, &rdev->flags)) {
    @@ -1533,7 +1533,7 @@ static void fix_read_error(conf_t *conf,

    rcu_read_lock();
    do {
    - int d = r10_bio->devs[sl].devnum;
    + d = r10_bio->devs[sl].devnum;
    rdev = rcu_dereference(conf->mirrors[d].rdev);
    if (rdev &&
    test_bit(In_sync, &rdev->flags)) {
    @@ -1567,7 +1567,7 @@ static void fix_read_error(conf_t *conf,
    rcu_read_lock();
    while (sl != r10_bio->read_slot) {
    char b[BDEVNAME_SIZE];
    - int d;
    +
    if (sl==0)
    sl = conf->copies;
    sl--;
    @@ -1603,7 +1603,7 @@ static void fix_read_error(conf_t *conf,
    }
    sl = start;
    while (sl != r10_bio->read_slot) {
    - int d;
    +
    if (sl==0)
    sl = conf->copies;
    sl--;



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