4.4-stable review patch. If anyone has any objections, please let me know.
------------------
From: Viktor Slavkovic <viktors@xxxxxxxxxx>
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@xxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
drivers/staging/android/ashmem.c | 2 ++
1 file changed, 2 insertions(+)
--- a/drivers/staging/android/ashmem.c
+++ b/drivers/staging/android/ashmem.c
@@ -759,10 +759,12 @@ 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;