[PATCH 4.20 17/76] staging: android: ashmem: Avoid range_alloc() allocation with ashmem_mutex held.

Greg Kroah-Hartman
2019-03-08T12:54:01Z

From: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>

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>

---
drivers/staging/android/ashmem.c | 42 ++++++++++++++++++++++-----------------
1 file changed, 24 insertions(+), 18 deletions(-)

--- a/drivers/staging/android/ashmem.c
+++ b/drivers/staging/android/ashmem.c
@@ -171,19 +171,15 @@ static inline void lru_del(struct ashmem
* @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_are

if (range_on_lru(range))
lru_add(range);
-
- return 0;
}

/**
@@ -596,7 +590,8 @@ static int get_name(struct ashmem_area *
*
* 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
* 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
*
* 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 ashme
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 ashme

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 ashme

out_unlock:
mutex_unlock(&ashmem_mutex);
+ if (range)
+ kmem_cache_free(ashmem_range_cachep, range);

return ret;
}