Patch "staging: android: ashmem: fix a race condition in ASHMEM_SET_SIZE ioctl" 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

staging: android: ashmem: fix a race condition in ASHMEM_SET_SIZE ioctl

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-ashmem_set_size-ioctl.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: Viktor Slavkovic <[email protected]>
Date: Mon, 8 Jan 2018 10:43:03 -0800
Subject: staging: android: ashmem: fix a race condition in ASHMEM_SET_SIZE ioctl

From: Viktor Slavkovic <[email protected]>

commit 443064cb0b1fb4569fe0a71209da7625129fb760 upstream.

A lock-unlock is missing in ASHMEM_SET_SIZE ioctl which can result in a race condition when mmap is called. After the !asma->file check, before setting asma->size, asma->file can be set in mmap. That would result in having different asma->size than the mapped memory size. Combined with ASHMEM_UNPIN ioctl and shrinker invocation, this can result in memory corruption.

---
 drivers/staging/android/ashmem.c |    2 ++
 1 file changed, 2 insertions(+)

@@ -774,10 +774,12 @@ static long ashmem_ioctl(struct file *fi
 		break;
 	case ASHMEM_SET_SIZE:
 		ret = -EINVAL;
+		mutex_lock(&ashmem_mutex);
 		if (!asma->file) {
 			ret = 0;
 			asma->size = (size_t)arg;
 		}
+		mutex_unlock(&ashmem_mutex);
 		break;
 	case ASHMEM_GET_SIZE:
 		ret = asma->size;

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

queue-4.9/staging-android-ashmem-fix-a-race-condition-in-ashmem_set_size-ioctl.patch