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Subject[PATCH] staging: android: ashmem: Remove deadlock
Date
Regression introduced in commit ce8a3a9e76d0193e2e8d74a06d275b3c324ca652
("staging: android: ashmem: Fix a race condition in pin ioctls")
causing deadlock.

No need to hold ashmem_mutex while copying from user

Stacks are:

ashmem_mmap+0x53/0x400 drivers/staging/android/ashmem.c:379
mmap_region+0x7dd/0xfd0 mm/mmap.c:1694
do_mmap+0x57b/0xbe0 mm/mmap.c:1473

and

lock_acquire+0x12e/0x410 kernel/locking/lockdep.c:3756
__might_fault+0x14a/0x1d0 mm/memory.c:4014
copy_from_user arch/x86/include/asm/uaccess.h:705 [inline]
ashmem_pin_unpin drivers/staging/android/ashmem.c:719 [inline]

Signed-off-by: Paul Lawrence <paullawrence@google.com>
Cc: <stable@vger.kernel.org> # 4.9.x
Cc: <stable@vger.kernel.org> # 4.4.x
Cc: <stable@vger.kernel.org> # 3.18.x: ce8a3a9e76d01
Cc: <stable@vger.kernel.org> # 3.18.x
Cc: Ben Hutchings <ben@decadent.org.uk>
---
drivers/staging/android/ashmem.c | 8 +++-----
1 file changed, 3 insertions(+), 5 deletions(-)

diff --git a/drivers/staging/android/ashmem.c b/drivers/staging/android/ashmem.c
index 6dbba5aff191..8c55706c2cfa 100644
--- a/drivers/staging/android/ashmem.c
+++ b/drivers/staging/android/ashmem.c
@@ -702,16 +702,14 @@ 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;
--
2.16.2.395.g2e18187dfd-goog
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