[libata] fix Null pointer dereference on disk error

Following oops were observed when disk error happened:

[ 4272.896937] sd 0:0:0:0: [sda] Unhandled error code
[ 4272.896939] sd 0:0:0:0: [sda] Result: hostbyte=DID_BAD_TARGET driverbyte=DRIVER_OK
[ 4272.896942] sd 0:0:0:0: [sda] CDB: Read(10): 28 00 00 5a de a7 00 00 08 00
[ 4272.896951] end_request: I/O error, dev sda, sector 5955239
[ 4291.574947] BUG: unable to handle kernel NULL pointer dereference at (null)
[ 4291.658305] IP: [] ahci_activity_show+0x1/0x40
[ 4291.730090] PGD 76dbbc067 PUD 6c4fba067 PMD 0
[ 4291.783408] Oops: 0000 [#1] SMP
[ 4291.822100] last sysfs file: /sys/devices/pci0000:00/0000:00:1f.2/host0/target0:0:0/0:0:0:0/sw_activity
[ 4291.934235] CPU 9
[ 4291.958301] Pid: 27942, comm: hwinfo ......

ata_scsi_find_dev could return NULL, so ata_scsi_activity_{show,store} should check if atadev is NULL.

Signed-off-by: Xiaotian Feng <dannyfeng@tencent.com>
Cc: James Bottomley <JBottomley@Parallels.com>
Cc: stable@kernel.org
Signed-off-by: Jeff Garzik <jgarzik@redhat.com>

diff --git a/drivers/ata/libata-scsi.c b/drivers/ata/libata-scsi.c
index a6df6a351d6e4ce263f717ad52bf1ebb72a1aae0..7c337e754dab30cf63c1b8a8b28c416f535bd86f 100644 (file)
--- a/drivers/ata/libata-scsi.c
+++ b/drivers/ata/libata-scsi.c
@@ -309,7 +309,8 @@ ata_scsi_activity_show(struct device *dev, struct device_attribute *attr,
        struct ata_port *ap = ata_shost_to_port(sdev->host);
        struct ata_device *atadev = ata_scsi_find_dev(ap, sdev);
 
-       if (ap->ops->sw_activity_show && (ap->flags & ATA_FLAG_SW_ACTIVITY))
+       if (atadev && ap->ops->sw_activity_show &&
+           (ap->flags & ATA_FLAG_SW_ACTIVITY))
                return ap->ops->sw_activity_show(atadev, buf);
        return -EINVAL;
 }
@@ -324,7 +325,8 @@ ata_scsi_activity_store(struct device *dev, struct device_attribute *attr,
        enum sw_activity val;
        int rc;
 
-       if (ap->ops->sw_activity_store && (ap->flags & ATA_FLAG_SW_ACTIVITY)) {
+       if (atadev && ap->ops->sw_activity_store &&
+           (ap->flags & ATA_FLAG_SW_ACTIVITY)) {
                val = simple_strtoul(buf, NULL, 0);
                switch (val) {
                case OFF: case BLINK_ON: case BLINK_OFF: