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staging: android: ashmem: Fix a race condition in pin ioctls

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ashmem_pin_unpin() reads asma->file and asma->size before taking the
ashmem_mutex, so it can race with other operations that modify them.

Build-tested only.

Cc: stable@vger.kernel.org
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Ben Hutchings 2018-02-04 02:06:27 +00:00 committed by Greg Kroah-Hartman
parent 02b7b2844c
commit ce8a3a9e76
1 changed files with 12 additions and 9 deletions
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21
drivers/staging/android/ashmem.c
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@ -702,30 +702,32 @@ static int ashmem_pin_unpin(struct ashmem_area *asma, unsigned long cmd,
size_t pgstart, pgend;
int ret = -EINVAL;
if (unlikely(!asma->file))
return -EINVAL;
mutex_lock(&ashmem_mutex);
if (unlikely(copy_from_user(&pin, p, sizeof(pin))))
return -EFAULT;
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;
if (unlikely((pin.offset | pin.len) & ~PAGE_MASK))
return -EINVAL;
goto out_unlock;
if (unlikely(((__u32)-1) - pin.offset < pin.len))
return -EINVAL;
goto out_unlock;
if (unlikely(PAGE_ALIGN(asma->size) < pin.offset + pin.len))
return -EINVAL;
goto out_unlock;
pgstart = pin.offset / PAGE_SIZE;
pgend = pgstart + (pin.len / PAGE_SIZE) - 1;
mutex_lock(&ashmem_mutex);
switch (cmd) {
case ASHMEM_PIN:
ret = ashmem_pin(asma, pgstart, pgend);
@ -738,6 +740,7 @@ static int ashmem_pin_unpin(struct ashmem_area *asma, unsigned long cmd,
break;
}
out_unlock:
mutex_unlock(&ashmem_mutex);
return ret;