Patch "staging: android: ashmem: Fix a race condition in pin ioctls" has been added to the 4.9-stable tree

[<gregkh@linuxfoundation.org>]

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

    staging: android: ashmem: Fix a race condition in pin ioctls

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:
     staging-android-ashmem-fix-a-race-condition-in-pin-ioctls.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 <stable@vger.kernel.org> know about it.


>From ce8a3a9e76d0193e2e8d74a06d275b3c324ca652 Mon Sep 17 00:00:00 2001
From: Ben Hutchings <ben@decadent.org.uk>
Date: Sun, 4 Feb 2018 02:06:27 +0000
Subject: staging: android: ashmem: Fix a race condition in pin ioctls

From: Ben Hutchings <ben@decadent.org.uk>

commit ce8a3a9e76d0193e2e8d74a06d275b3c324ca652 upstream.

ashmem_pin_unpin() reads asma->file and asma->size before taking the
ashmem_mutex, so it can race with other operations that modify them.

Build-tested only.

Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
 drivers/staging/android/ashmem.c |   19 +++++++++++--------
 1 file changed, 11 insertions(+), 8 deletions(-)

--- a/drivers/staging/android/ashmem.c
+++ b/drivers/staging/android/ashmem.c
@@ -719,30 +719,32 @@ static int ashmem_pin_unpin(struct ashme
 	size_t pgstart, pgend;
 	int ret = -EINVAL;
 
+	mutex_lock(&ashmem_mutex);
+
 	if (unlikely(!asma->file))
-		return -EINVAL;
+		goto out_unlock;
 
-	if (unlikely(copy_from_user(&pin, p, sizeof(pin))))
-		return -EFAULT;
+	if (unlikely(copy_from_user(&pin, p, sizeof(pin)))) {
+		ret = -EFAULT;
+		goto out_unlock;
+	}
 
 	/* per custom, you can pass zero for len to mean "everything onward" */
 	if (!pin.len)
 		pin.len = PAGE_ALIGN(asma->size) - pin.offset;
 
 	if (unlikely((pin.offset | pin.len) & ~PAGE_MASK))
-		return -EINVAL;
+		goto out_unlock;
 
 	if (unlikely(((__u32)-1) - pin.offset < pin.len))
-		return -EINVAL;
+		goto out_unlock;
 
 	if (unlikely(PAGE_ALIGN(asma->size) < pin.offset + pin.len))
-		return -EINVAL;
+		goto out_unlock;
 
 	pgstart = pin.offset / PAGE_SIZE;
 	pgend = pgstart + (pin.len / PAGE_SIZE) - 1;
 
-	mutex_lock(&ashmem_mutex);
-
 	switch (cmd) {
 	case ASHMEM_PIN:
 		ret = ashmem_pin(asma, pgstart, pgend);
@@ -755,6 +757,7 @@ static int ashmem_pin_unpin(struct ashme
 		break;
 	}
 
+out_unlock:
 	mutex_unlock(&ashmem_mutex);
 
 	return ret;


Patches currently in stable-queue which might be from ben@decadent.org.uk are

queue-4.9/staging-android-ashmem-fix-a-race-condition-in-pin-ioctls.patch