md: raid10: Fix null pointer dereference in fix_read_error()

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().

Cc: stable@kernel.org
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>

1 files changed, 6 insertions, 6 deletions

diff --git a/drivers/md/raid10.c b/drivers/md/raid10.c
index 03724992cdf2..6d420cb487b5 100644
--- a/drivers/md/raid10.c
+++ b/drivers/md/raid10.c
@@ -1482,14 +1482,14 @@ static void fix_read_error(conf_t *conf, mddev_t *mddev, r10bio_t *r10_bio)
         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)) {
@@ -1530,7 +1530,7 @@ static void fix_read_error(conf_t *conf, mddev_t *mddev, r10bio_t *r10_bio)
 
                 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)) {
@@ -1564,7 +1564,7 @@ static void fix_read_error(conf_t *conf, mddev_t *mddev, r10bio_t *r10_bio)
                 rcu_read_lock();
                 while (sl != r10_bio->read_slot) {
                         char b[BDEVNAME_SIZE];
-                        int d;
+
                         if (sl==0)
                                 sl = conf->copies;
                         sl--;
@@ -1601,7 +1601,7 @@ static void fix_read_error(conf_t *conf, mddev_t *mddev, r10bio_t *r10_bio)
                 }
                 sl = start;
                 while (sl != r10_bio->read_slot) {
-                        int d;
+
                         if (sl==0)
                                 sl = conf->copies;
                         sl--;