scsi: CVE-2018-20836

scsi: libsas: fix a race condition when smp task timeout

References:
https://nvd.nist.gov/vuln/detail/CVE-2018-20836
https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?h=linux-4.9.y&id=41b5d3eee4af6a4ea488a1735ed82e4e593eec0d

Change-Id: I6bd1bfbad5358379ead43314c780859b1d11e658
Signed-off-by: Andreas Wellving <andreas.wellving@enea.com>

2 files changed, 74 insertions, 0 deletions

diff --git a/patches/cve/4.9.x.scc b/patches/cve/4.9.x.scc
index 6259efc..a1c8ba5 100644
--- a/patches/cve/4.9.x.scc
+++ b/patches/cve/4.9.x.scc
@@ -75,3 +75,6 @@ patch CVE-2019-8980-exec-Fix-mem-leak-in-kernel_read_file.patch
 
 #CVEs fixed in 4.9.169:
 patch CVE-2019-11815-net-rds-force-to-destroy-connection-if-t_sock-is-NUL.patch
+
+#CVEs fixed in 4.9.175:
+patch CVE-2018-20836-scsi-libsas-fix-a-race-condition-when-smp-task-timeo.patch
diff --git a/patches/cve/CVE-2018-20836-scsi-libsas-fix-a-race-condition-when-smp-task-timeo.patch b/patches/cve/CVE-2018-20836-scsi-libsas-fix-a-race-condition-when-smp-task-timeo.patch
new file mode 100644
index 0000000..dc9f8f8
--- /dev/null
+++ b/patches/cve/CVE-2018-20836-scsi-libsas-fix-a-race-condition-when-smp-task-timeo.patch
@@ -0,0 +1,71 @@
+From 41b5d3eee4af6a4ea488a1735ed82e4e593eec0d Mon Sep 17 00:00:00 2001
+From: Jason Yan <yanaijie@huawei.com>
+Date: Tue, 25 Sep 2018 10:56:54 +0800
+Subject: [PATCH] scsi: libsas: fix a race condition when smp task timeout
+
+commit b90cd6f2b905905fb42671009dc0e27c310a16ae upstream.
+
+When the lldd is processing the complete sas task in interrupt and set the
+task stat as SAS_TASK_STATE_DONE, the smp timeout timer is able to be
+triggered at the same time. And smp_task_timedout() will complete the task
+wheter the SAS_TASK_STATE_DONE is set or not. Then the sas task may freed
+before lldd end the interrupt process. Thus a use-after-free will happen.
+
+Fix this by calling the complete() only when SAS_TASK_STATE_DONE is not
+set. And remove the check of the return value of the del_timer(). Once the
+LLDD sets DONE, it must call task->done(), which will call
+smp_task_done()->complete() and the task will be completed and freed
+correctly.
+
+CVE: CVE-2018-20836
+Upstream-Status: Backport [https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?h=linux-4.9.y&id=41b5d3eee4af6a4ea488a1735ed82e4e593eec0d]
+
+Reported-by: chenxiang <chenxiang66@hisilicon.com>
+Signed-off-by: Jason Yan <yanaijie@huawei.com>
+CC: John Garry <john.garry@huawei.com>
+CC: Johannes Thumshirn <jthumshirn@suse.de>
+CC: Ewan Milne <emilne@redhat.com>
+CC: Christoph Hellwig <hch@lst.de>
+CC: Tomas Henzl <thenzl@redhat.com>
+CC: Dan Williams <dan.j.williams@intel.com>
+CC: Hannes Reinecke <hare@suse.com>
+Reviewed-by: Hannes Reinecke <hare@suse.com>
+Reviewed-by: John Garry <john.garry@huawei.com>
+Reviewed-by: Johannes Thumshirn <jthumshirn@suse.de>
+Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>
+Cc: Guenter Roeck <linux@roeck-us.net
+Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
+Signed-off-by: Andreas Wellving <andreas.wellving@enea.com>
+---
+ drivers/scsi/libsas/sas_expander.c | 9 ++++-----
+ 1 file changed, 4 insertions(+), 5 deletions(-)
+
+diff --git a/drivers/scsi/libsas/sas_expander.c b/drivers/scsi/libsas/sas_expander.c
+index 7be581f7c35d..1a6f65db615e 100644
+--- a/drivers/scsi/libsas/sas_expander.c
++++ b/drivers/scsi/libsas/sas_expander.c
+@@ -47,17 +47,16 @@ static void smp_task_timedout(unsigned long _task)
+        unsigned long flags;
+ 
+        spin_lock_irqsave(&task->task_state_lock, flags);
+-       if (!(task->task_state_flags & SAS_TASK_STATE_DONE))
++       if (!(task->task_state_flags & SAS_TASK_STATE_DONE)) {
+                task->task_state_flags |= SAS_TASK_STATE_ABORTED;
++               complete(&task->slow_task->completion);
++       }
+        spin_unlock_irqrestore(&task->task_state_lock, flags);
+-
+-       complete(&task->slow_task->completion);
+ }
+ 
+ static void smp_task_done(struct sas_task *task)
+ {
+-       if (!del_timer(&task->slow_task->timer))
+-               return;
++       del_timer(&task->slow_task->timer);
+        complete(&task->slow_task->completion);
+ }
+ 
+-- 
+2.20.1
+