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

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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>
Cc: stable@vger.kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Viktor Slavkovic 2018-01-08 10:43:03 -08:00 committed by Greg Kroah-Hartman
parent 30a7acd573
commit 443064cb0b
1 changed files with 2 additions and 0 deletions
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2
drivers/staging/android/ashmem.c
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@ -765,10 +765,12 @@ static long ashmem_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
break; break;
case ASHMEM_SET_SIZE: case ASHMEM_SET_SIZE:
ret = -EINVAL; ret = -EINVAL;
mutex_lock(&ashmem_mutex);
if (!asma->file) { if (!asma->file) {
ret = 0; ret = 0;
asma->size = (size_t)arg; asma->size = (size_t)arg;
} }
mutex_unlock(&ashmem_mutex);
break; break;
case ASHMEM_GET_SIZE: case ASHMEM_GET_SIZE:
ret = asma->size; ret = asma->size;