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From: Srinivas Kandagatla <>
Cc:, Ola Jeppsson <>,
	Abel Vesa <>,
	Srinivas Kandagatla <>
Subject: [PATCH 3/3] misc: fastrpc: Fix use-after-free race condition for maps
Date: Thu, 24 Nov 2022 17:49:41 +0000	[thread overview]
Message-ID: <> (raw)
In-Reply-To: <>

From: Ola Jeppsson <>

It is possible that in between calling fastrpc_map_get() until
map->fl->lock is taken in fastrpc_free_map(), another thread can call
fastrpc_map_lookup() and get a reference to a map that is about to be

Rewrite fastrpc_map_get() to only increase the reference count of a map
if it's non-zero. Propagate this to callers so they can know if a map is
about to be deleted.

Fixes this warning:
refcount_t: addition on 0; use-after-free.
WARNING: CPU: 5 PID: 10100 at lib/refcount.c:25 refcount_warn_saturate
Call trace:
 [fastrpc_map_get inlined]
 [fastrpc_map_lookup inlined]

Fixes: c68cfb718c8f ("misc: fastrpc: Add support for context Invoke method")
Signed-off-by: Ola Jeppsson <>
Signed-off-by: Abel Vesa <>
Signed-off-by: Srinivas Kandagatla <>
 drivers/misc/fastrpc.c | 8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/drivers/misc/fastrpc.c b/drivers/misc/fastrpc.c
index 9ecbf673d321..80811e852d8f 100644
--- a/drivers/misc/fastrpc.c
+++ b/drivers/misc/fastrpc.c
@@ -332,10 +332,12 @@ static void fastrpc_map_put(struct fastrpc_map *map)
 		kref_put(&map->refcount, fastrpc_free_map);
-static void fastrpc_map_get(struct fastrpc_map *map)
+static int fastrpc_map_get(struct fastrpc_map *map)
-	if (map)
-		kref_get(&map->refcount);
+	if (!map)
+		return -ENOENT;
+	return kref_get_unless_zero(&map->refcount) ? 0 : -ENOENT;

  parent reply	other threads:[~2022-11-24 17:50 UTC|newest]

Thread overview: 6+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2022-11-24 17:49 [PATCH 0/3] misc: fastrpc: fixes for 6.1 Srinivas Kandagatla
2022-11-24 17:49 ` [PATCH 1/3] misc: fastrpc: Fix use-after-free and race in fastrpc_map_find Srinivas Kandagatla
2022-11-24 17:49 ` [PATCH 2/3] misc: fastrpc: Don't remove map on creater_process and device_release Srinivas Kandagatla
2022-11-24 17:49 ` Srinivas Kandagatla [this message]
  -- strict thread matches above, loose matches on Subject: below --
2022-09-02 15:14 [PATCH 1/3] misc: fastrpc: Fix use-after-free and race in fastrpc_map_find Abel Vesa
2022-09-02 15:14 ` [PATCH 3/3] misc: fastrpc: Fix use-after-free race condition for maps Abel Vesa
2022-09-22 22:45   ` Srinivas Kandagatla

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