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From: Greg KH on 30 Jul 2010 14:30
2.6.34-stable review patch. If anyone has any objections, please let us know.

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

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

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

--- a/drivers/md/raid10.c
+++ b/drivers/md/raid10.c
@@ -1487,14 +1487,14 @@ 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)) {
@@ -1534,7 +1534,7 @@ 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)) {
@@ -1568,7 +1568,7 @@ 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--;
@@ -1604,7 +1604,7 @@ 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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