From 09fa66ec1b4896ab841da085ca58b6433f28f07f Mon Sep 17 00:00:00 2001 From: Yifei Gao Date: Fri, 2 Oct 2026 11:12:19 +0100 Subject: [PATCH] misc: fastrpc: fix double-free in fastrpc_map_attach() error path 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 Reviewed-by: Ekansh Gupta Signed-off-by: Srinivas Kandagatla Link: https://patch.msgid.link/20261002101220.1084101-2-srinivas.kandagatla@oss.qualcomm.com Signed-off-by: Greg Kroah-Hartman --- 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 53ad9a3f1069..904f538f0dd0 100644 --- a/drivers/misc/fastrpc.c +++ b/drivers/misc/fastrpc.c @@ -927,7 +927,7 @@ 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; @@ -950,7 +950,7 @@ 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);