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authorYisheng Xie <xieyisheng1@huawei.com>2018-02-28 14:59:22 +0800
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>2018-03-06 07:21:10 -0800
commit740a5759bf222332fbb5eda42f89aa25ba38f9b2 (patch)
tree98249dca5eb2862055a4102d2ca8526bc4359c17 /drivers/staging/android
parenta42ae5905140c324362fe5036ae1dbb16e4d359c (diff)
staging: android: ashmem: Fix possible deadlock in ashmem_ioctl
ashmem_mutex may create a chain of dependencies like: CPU0 CPU1 mmap syscall ioctl syscall -> mmap_sem (acquired) -> ashmem_ioctl -> ashmem_mmap -> ashmem_mutex (acquired) -> ashmem_mutex (try to acquire) -> copy_from_user -> mmap_sem (try to acquire) There is a lock odering problem between mmap_sem and ashmem_mutex causing a lockdep splat[1] during a syzcaller test. This patch fixes the problem by move copy_from_user out of ashmem_mutex. [1] https://www.spinics.net/lists/kernel/msg2733200.html Fixes: ce8a3a9e76d0 (staging: android: ashmem: Fix a race condition in pin ioctls) Reported-by: syzbot+d7a918a7a8e1c952bc36@syzkaller.appspotmail.com Signed-off-by: Yisheng Xie <xieyisheng1@huawei.com> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Diffstat (limited to 'drivers/staging/android')
-rw-r--r--drivers/staging/android/ashmem.c8
1 files changed, 3 insertions, 5 deletions
diff --git a/drivers/staging/android/ashmem.c b/drivers/staging/android/ashmem.c
index d5450365769c..86580b6df33d 100644
--- a/drivers/staging/android/ashmem.c
+++ b/drivers/staging/android/ashmem.c
@@ -701,16 +701,14 @@ static int ashmem_pin_unpin(struct ashmem_area *asma, unsigned long cmd,
size_t pgstart, pgend;
int ret = -EINVAL;
+ if (unlikely(copy_from_user(&pin, p, sizeof(pin))))
+ return -EFAULT;
+
mutex_lock(&ashmem_mutex);
if (unlikely(!asma->file))
goto out_unlock;
- if (unlikely(copy_from_user(&pin, p, sizeof(pin)))) {
- ret = -EFAULT;
- goto out_unlock;
- }
-
/* per custom, you can pass zero for len to mean "everything onward" */
if (!pin.len)
pin.len = PAGE_ALIGN(asma->size) - pin.offset;