[PATCH 6.12.y 2/2] misc: fastrpc: fix double-free in fastrpc_map_attach() error path

[Sasha Levin <sashal@kernel.org>]

From: Yifei Gao <gyf161023@gmail.com>

[ Upstream commit 09fa66ec1b4896ab841da085ca58b6433f28f07f ]

map->table is assigned right after dma_buf_map_attachment_unlocked()
succeeds. The two failure checks that follow, the len > map->size test
and, where subsystem VMIDs are configured, a failed qcom_scm_assign_mem(),
jump to map_err with map->table already set.

map_err manually calls dma_buf_detach() and dma_buf_put() and then falls
through to fastrpc_map_put(). Since that change the error path tail is
fastrpc_map_put() -> fastrpc_free_map(), and fastrpc_free_map() already
unmaps, detaches and puts the dma-buf whenever map->table is set.
The two operations therefore run twice: the second dma_buf_put() drops an
extra reference on map->buf, and dma_buf_unmap_attachment_unlocked()
dereferences the map->attach already freed by the manual dma_buf_detach().
kref_init() sets the refcount to 1 with no intervening get, so the final
fastrpc_map_put() frees the map synchronously and the redundant cleanup is
deterministic.

The len > map->size branch is reachable by an unprivileged process via
FASTRPC_IOCTL_MEM_MAP with an fd whose dma-buf is smaller than the
requested length, before any DSP invocation.

Route both map->table-is-set failure branches to get_err instead of
map_err, so fastrpc_free_map() is the single owner of the
unmap/detach/put sequence. map_err is retained for the
dma_buf_map_attachment_unlocked() failure, which is reached with
map->table still NULL and an attachment that fastrpc_free_map() will not
clean up, so its dma_buf_detach()/dma_buf_put() must still run manually.

Fixes: 334f1a1cbe03 ("misc: fastrpc: Use fastrpc_map_put in fastrpc_map_create on fail")
Cc: stable@vger.kernel.org
Assisted-by: Claude:claude-opus-4-8
Signed-off-by: Yifei Gao <gyf161023@gmail.com>
Reviewed-by: Ekansh Gupta <ekansh.gupta@oss.qualcomm.com>
Signed-off-by: Srinivas Kandagatla <srini@kernel.org>
Link: https://patch.msgid.link/20261002101220.1084101-2-srinivas.kandagatla@oss.qualcomm.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 drivers/misc/fastrpc.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/misc/fastrpc.c b/drivers/misc/fastrpc.c
index afafaa68e2bd2..a4577ef5a3946 100644
--- a/drivers/misc/fastrpc.c
+++ b/drivers/misc/fastrpc.c
@@ -857,7 +857,7 @@ static int fastrpc_map_attach(struct fastrpc_user *fl, int fd,
 		dev_dbg(sess->dev, "Bad size passed len 0x%llx map size 0x%llx\n",
 				len, map->size);
 		err = -EINVAL;
-		goto map_err;
+		goto get_err;
 	}
 	map->va = sg_virt(map->table->sgl);
 	map->len = len;
@@ -880,7 +880,7 @@ static int fastrpc_map_attach(struct fastrpc_user *fl, int fd,
 			dev_err(sess->dev,
 				"Failed to assign memory with dma_addr %pad size 0x%llx err %d\n",
 				&map->dma_addr, map->len, err);
-			goto map_err;
+			goto get_err;
 		}
 	}
 	spin_lock(&fl->lock);
-- 
2.53.0