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SubjectRe: [PATCH] staging: android: ashmem: Remove deadlock
On Wed, Mar 07, 2018 at 01:40:30PM -0800, Paul Lawrence wrote:
> 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
>

Hey Paul,

Looks like this same patch is already in Greg's tree:
https://git.kernel.org/pub/scm/linux/kernel/git/gregkh/staging.git/commit/?id=740a5759bf222332fbb5eda42f89aa25ba38f9b2

Cheers!
Nathan Chancellor

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