From: Viktor Slavkovic <viktors@google.com>
Date: Mon, 8 Jan 2018 18:43:03 +0000 (-0800)
Subject: staging: android: ashmem: fix a race condition in ASHMEM_SET_SIZE ioctl
X-Git-Tag: v4.4.112~17
X-Git-Url: http://git.ipfire.org/gitweb.cgi?a=commitdiff_plain;h=b4106c55b574fe37900b02ddf89cbe4b9d971392;p=thirdparty%2Fkernel%2Fstable.git

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>
---

diff --git a/drivers/staging/android/ashmem.c b/drivers/staging/android/ashmem.c
index 9c6357c03905d..b64327722660e 100644
--- a/drivers/staging/android/ashmem.c
+++ b/drivers/staging/android/ashmem.c
@@ -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;