Patch "scsi: qla2xxx: Get mutex lock before checking optrom_state" has been added to the 4.9-stable tree

This is a note to let you know that I've just added the patch titled

scsi: qla2xxx: Get mutex lock before checking optrom_state

to the 4.9-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
scsi-qla2xxx-get-mutex-lock-before-checking-optrom_state.patch
and it can be found in the queue-4.9 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: "Milan P. Gandhi" <[email protected]>
Date: Sat, 24 Dec 2016 22:02:46 +0530
Subject: scsi: qla2xxx: Get mutex lock before checking optrom_state

From: "Milan P. Gandhi" <[email protected]>

[ Upstream commit c7702b8c22712a06080e10f1d2dee1a133ec8809 ]

There is a race condition with qla2xxx optrom functions where one thread might modify optrom buffer, optrom_state while other thread is still reading from it.

In couple of crashes, it was found that we had successfully passed the following 'if' check where we confirm optrom_state to be QLA_SREADING. But by the time we acquired mutex lock to proceed with memory_read_from_buffer function, some other thread/process had already modified that option rom buffer and optrom_state from QLA_SREADING to QLA_SWAITING. Then we got ha->optrom_buffer 0x0 and crashed the system:

        if (ha->optrom_state != QLA_SREADING)
                return 0;

        mutex_lock(&ha->optrom_mutex);
        rval = memory_read_from_buffer(buf, count, &off, ha->optrom_buffer,
            ha->optrom_region_size);
        mutex_unlock(&ha->optrom_mutex);

With current optrom function we get following crash due to a race condition:

[ 1479.466679] BUG: unable to handle kernel NULL pointer dereference at           (null)
[ 1479.466707] IP: [<ffffffff81326756>] memcpy+0x6/0x110
[...]
[ 1479.473673] Call Trace:
[ 1479.474296]  [<ffffffff81225cbc>] ? memory_read_from_buffer+0x3c/0x60
[ 1479.474941]  [<ffffffffa01574dc>] qla2x00_sysfs_read_optrom+0x9c/0xc0 [qla2xxx]
[ 1479.475571]  [<ffffffff8127e76b>] read+0xdb/0x1f0
[ 1479.476206]  [<ffffffff811fdf9e>] vfs_read+0x9e/0x170
[ 1479.476839]  [<ffffffff811feb6f>] SyS_read+0x7f/0xe0
[ 1479.477466]  [<ffffffff816964c9>] system_call_fastpath+0x16/0x1b

Below patch modifies qla2x00_sysfs_read_optrom, qla2x00_sysfs_write_optrom functions to get the mutex_lock before checking ha->optrom_state to avoid similar crashes.

The patch was applied and tested and same crashes were no longer observed again.

---
 drivers/scsi/qla2xxx/qla_attr.c |   18 +++++++++++++-----
 1 file changed, 13 insertions(+), 5 deletions(-)

@@ -243,12 +243,15 @@ qla2x00_sysfs_read_optrom(struct file *f
 	struct qla_hw_data *ha = vha->hw;
 	ssize_t rval = 0;
 
+	mutex_lock(&ha->optrom_mutex);
+
 	if (ha->optrom_state != QLA_SREADING)
-		return 0;
+		goto out;
 
-	mutex_lock(&ha->optrom_mutex);
 	rval = memory_read_from_buffer(buf, count, &off, ha->optrom_buffer,
 	    ha->optrom_region_size);
+
+out:
 	mutex_unlock(&ha->optrom_mutex);
 
 	return rval;

@@ -263,14 +266,19 @@ qla2x00_sysfs_write_optrom(struct file *
 	    struct device, kobj)));
 	struct qla_hw_data *ha = vha->hw;
 
-	if (ha->optrom_state != QLA_SWRITING)
+	mutex_lock(&ha->optrom_mutex);
+
+	if (ha->optrom_state != QLA_SWRITING) {
+		mutex_unlock(&ha->optrom_mutex);
 		return -EINVAL;
-	if (off > ha->optrom_region_size)
+	}
+	if (off > ha->optrom_region_size) {
+		mutex_unlock(&ha->optrom_mutex);
 		return -ERANGE;
+	}
 	if (off + count > ha->optrom_region_size)
 		count = ha->optrom_region_size - off;
 
-	mutex_lock(&ha->optrom_mutex);
 	memcpy(&ha->optrom_buffer[off], buf, count);
 	mutex_unlock(&ha->optrom_mutex);
 

Patches currently in stable-queue which might be from [email protected] are

queue-4.9/scsi-qla2xxx-get-mutex-lock-before-checking-optrom_state.patch