This is a note to let you know that I've just added the patch titled misc: fastrpc: Fix use-after-free race condition for maps to the 5.4-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary The filename of the patch is: misc-fastrpc-fix-use-after-free-race-condition-for-maps.patch and it can be found in the queue-5.4 subdirectory. If you, or anyone else, feels it should not be added to the stable tree, please let <stable@xxxxxxxxxxxxxxx> know about it. >From 96b328d119eca7563c1edcc4e1039a62e6370ecb Mon Sep 17 00:00:00 2001 From: Ola Jeppsson <ola@xxxxxxxx> Date: Thu, 24 Nov 2022 17:49:41 +0000 Subject: misc: fastrpc: Fix use-after-free race condition for maps From: Ola Jeppsson <ola@xxxxxxxx> commit 96b328d119eca7563c1edcc4e1039a62e6370ecb upstream. 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 deleted. 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: refcount_warn_saturate [fastrpc_map_get inlined] [fastrpc_map_lookup inlined] fastrpc_map_create fastrpc_internal_invoke fastrpc_device_ioctl __arm64_sys_ioctl invoke_syscall Fixes: c68cfb718c8f ("misc: fastrpc: Add support for context Invoke method") Cc: stable <stable@xxxxxxxxxx> Signed-off-by: Ola Jeppsson <ola@xxxxxxxx> Signed-off-by: Abel Vesa <abel.vesa@xxxxxxxxxx> Signed-off-by: Srinivas Kandagatla <srinivas.kandagatla@xxxxxxxxxx> Link: https://lore.kernel.org/r/20221124174941.418450-4-srinivas.kandagatla@xxxxxxxxxx Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> --- drivers/misc/fastrpc.c | 8 +++++--- 1 file changed, 5 insertions(+), 3 deletions(-) --- a/drivers/misc/fastrpc.c +++ b/drivers/misc/fastrpc.c @@ -234,10 +234,12 @@ static void fastrpc_map_put(struct fastr 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; } static int fastrpc_map_find(struct fastrpc_user *fl, int fd, Patches currently in stable-queue which might be from ola@xxxxxxxx are queue-5.4/misc-fastrpc-don-t-remove-map-on-creater_process-and-device_release.patch queue-5.4/misc-fastrpc-fix-use-after-free-race-condition-for-maps.patch