On Fri, Feb 22, 2019 at 08:03:55PM +0900, Tetsuo Handa wrote:
> ashmem_pin() is calling range_shrink() without checking whether
> range_alloc() succeeded. Also, doing memory allocation with ashmem_mutex
> held should be avoided because ashmem_shrink_scan() tries to hold it.
>
> Therefore, move memory allocation for range_alloc() to ashmem_pin_unpin()
> and make range_alloc() not to fail.
>
> This patch is mostly meant for backporting purpose for fuzz testing on
> stable/distributor kernels, for there is a plan to remove this code in
> near future.
>
> Signed-off-by: Tetsuo Handa <penguin-kernel@xxxxxxxxxxxxxxxxxxx>
> Cc: stable@xxxxxxxxxxxxxxx
Reviewed-by: Joel Fernandes (Google) <joel@xxxxxxxxxxxxxxxxx>
thanks,
- Joel
> ---
> drivers/staging/android/ashmem.c | 42 +++++++++++++++++++++++-----------------
> 1 file changed, 24 insertions(+), 18 deletions(-)
>
> diff --git a/drivers/staging/android/ashmem.c b/drivers/staging/android/ashmem.c
> index 5d5b091..74d497d 100644
> --- a/drivers/staging/android/ashmem.c
> +++ b/drivers/staging/android/ashmem.c
> @@ -172,19 +172,15 @@ static inline void lru_del(struct ashmem_range *range)
> * @end: The ending page (inclusive)
> *
> * This function is protected by ashmem_mutex.
> - *
> - * Return: 0 if successful, or -ENOMEM if there is an error
> */
> -static int range_alloc(struct ashmem_area *asma,
> - struct ashmem_range *prev_range, unsigned int purged,
> - size_t start, size_t end)
> +static void range_alloc(struct ashmem_area *asma,
> + struct ashmem_range *prev_range, unsigned int purged,
> + size_t start, size_t end,
> + struct ashmem_range **new_range)
> {
> - struct ashmem_range *range;
> -
> - range = kmem_cache_zalloc(ashmem_range_cachep, GFP_KERNEL);
> - if (!range)
> - return -ENOMEM;
> + struct ashmem_range *range = *new_range;
>
> + *new_range = NULL;
> range->asma = asma;
> range->pgstart = start;
> range->pgend = end;
> @@ -194,8 +190,6 @@ static int range_alloc(struct ashmem_area *asma,
>
> if (range_on_lru(range))
> lru_add(range);
> -
> - return 0;
> }
>
> /**
> @@ -597,7 +591,8 @@ static int get_name(struct ashmem_area *asma, void __user *name)
> *
> * Caller must hold ashmem_mutex.
> */
> -static int ashmem_pin(struct ashmem_area *asma, size_t pgstart, size_t pgend)
> +static int ashmem_pin(struct ashmem_area *asma, size_t pgstart, size_t pgend,
> + struct ashmem_range **new_range)
> {
> struct ashmem_range *range, *next;
> int ret = ASHMEM_NOT_PURGED;
> @@ -650,7 +645,7 @@ static int ashmem_pin(struct ashmem_area *asma, size_t pgstart, size_t pgend)
> * second half and adjust the first chunk's endpoint.
> */
> range_alloc(asma, range, range->purged,
> - pgend + 1, range->pgend);
> + pgend + 1, range->pgend, new_range);
> range_shrink(range, range->pgstart, pgstart - 1);
> break;
> }
> @@ -664,7 +659,8 @@ static int ashmem_pin(struct ashmem_area *asma, size_t pgstart, size_t pgend)
> *
> * Caller must hold ashmem_mutex.
> */
> -static int ashmem_unpin(struct ashmem_area *asma, size_t pgstart, size_t pgend)
> +static int ashmem_unpin(struct ashmem_area *asma, size_t pgstart, size_t pgend,
> + struct ashmem_range **new_range)
> {
> struct ashmem_range *range, *next;
> unsigned int purged = ASHMEM_NOT_PURGED;
> @@ -690,7 +686,8 @@ static int ashmem_unpin(struct ashmem_area *asma, size_t pgstart, size_t pgend)
> }
> }
>
> - return range_alloc(asma, range, purged, pgstart, pgend);
> + range_alloc(asma, range, purged, pgstart, pgend, new_range);
> + return 0;
> }
>
> /*
> @@ -723,10 +720,17 @@ static int ashmem_pin_unpin(struct ashmem_area *asma, unsigned long cmd,
> struct ashmem_pin pin;
> size_t pgstart, pgend;
> int ret = -EINVAL;
> + struct ashmem_range *range = NULL;
>
> if (copy_from_user(&pin, p, sizeof(pin)))
> return -EFAULT;
>
> + if (cmd == ASHMEM_PIN || cmd == ASHMEM_UNPIN) {
> + range = kmem_cache_zalloc(ashmem_range_cachep, GFP_KERNEL);
> + if (!range)
> + return -ENOMEM;
> + }
> +
> mutex_lock(&ashmem_mutex);
> wait_event(ashmem_shrink_wait, !atomic_read(&ashmem_shrink_inflight));
>
> @@ -751,10 +755,10 @@ static int ashmem_pin_unpin(struct ashmem_area *asma, unsigned long cmd,
>
> switch (cmd) {
> case ASHMEM_PIN:
> - ret = ashmem_pin(asma, pgstart, pgend);
> + ret = ashmem_pin(asma, pgstart, pgend, &range);
> break;
> case ASHMEM_UNPIN:
> - ret = ashmem_unpin(asma, pgstart, pgend);
> + ret = ashmem_unpin(asma, pgstart, pgend, &range);
> break;
> case ASHMEM_GET_PIN_STATUS:
> ret = ashmem_get_pin_status(asma, pgstart, pgend);
> @@ -763,6 +767,8 @@ static int ashmem_pin_unpin(struct ashmem_area *asma, unsigned long cmd,
>
> out_unlock:
> mutex_unlock(&ashmem_mutex);
> + if (range)
> + kmem_cache_free(ashmem_range_cachep, range);
This seems a bit broken to me. Once a range has been added to the LRU list,
it is then being freed here. So then the ashmem_lru_list will contain a
dangling range, right?
I don't see much point in this patch.
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