Commit 6dc42f88 authored Jan 08, 2018 by Viktor Slavkovic Committed by Greg Kroah-Hartman Jan 17, 2018

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



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.

Signed-off-by: Viktor Slavkovic <viktors@google.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

parent f54053fa

drivers/staging/android/ashmem.c

+2 −0

Original line number	Diff line number	Diff line
		@@ -759,10 +759,12 @@ static long ashmem_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
		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;