staging: android: ashmem: Avoid range_alloc() allocation with ashmem_mutex held.

commit ecd182cbf4e107928077866399100228d2359c60 upstream.

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@I-love.SAKURA.ne.jp>
Cc: stable@vger.kernel.org
Reviewed-by: Joel Fernandes <joel@joelfernandes.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/staging/android/ashmem.c b/drivers/staging/android/ashmem.c
index 1cc451b..be81533 100644 (file)
--- a/drivers/staging/android/ashmem.c
+++ b/drivers/staging/android/ashmem.c
@@ -171,19 +171,15 @@ 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;
@@ -193,8 +189,6 @@ static int range_alloc(struct ashmem_area *asma,
 
        if (range_on_lru(range))
                lru_add(range);
-
-       return 0;
 }
 
 /**
@@ -596,7 +590,8 @@ 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;
@@ -649,7 +644,7 @@ 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;
                }
@@ -663,7 +658,8 @@ 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;
@@ -689,7 +685,8 @@ restart:
                }
        }
 
-       return range_alloc(asma, range, purged, pgstart, pgend);
+       range_alloc(asma, range, purged, pgstart, pgend, new_range);
+       return 0;
 }
 
 /*
@@ -722,10 +719,17 @@ 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));
 
@@ -750,10 +754,10 @@ 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);
@@ -762,6 +766,8 @@ 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);
 
        return ret;
 }