On Wed, Feb 20, 2013 at 05:53:59PM +0530, Shankar Brahadeeswaran wrote:
> static int set_name(struct ashmem_area *asma, void __user *name)
> {
> int ret = 0;
> -
> - mutex_lock(&ashmem_mutex);
> + char local_name[ASHMEM_NAME_LEN];
>
> /* cannot change an existing mapping's name */
> if (unlikely(asma->file)) {
> @@ -423,9 +422,22 @@ static int set_name(struct ashmem_area *asma, void
> __user *name)
> goto out;
You're not holding the lock here so you can return directly.
Otherwise it's a double unlock.
> }
>
> - if (unlikely(copy_from_user(asma->name + ASHMEM_NAME_PREFIX_LEN,
> - name, ASHMEM_NAME_LEN)))
> + /*
> + * Holding the ashmem_mutex while doing a copy_from_user might cause
> + * an data abourt which would try to access mmap_sem. If another
> + * thread has invoked ashmem_mmap then it will be holding the
> + * semaphore and will be waiting for ashmem_mutex, there by leading to
> + * deadlock. We'll release the mutex and take the name to a local
> + * variable that does not need protection and later copy the local
> + * variable to the structure member with lock held.
> + */
> + if (unlikely(copy_from_user(local_name, name, ASHMEM_NAME_LEN))) {
> ret = -EFAULT;
> + return ret;
return -EFAULT;
These weren't there in the original, only when you redid it at my
request. :/ Sorry for that.
regards,
dan carpenter
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