[PATCH] misc: fastrpc: fix use-after-free in fastrpc_map_attach() error path

map->table is set right after the attachment is mapped, before the
len > map->size check. When that check fails and jumps to map_err, the
error path manually calls dma_buf_detach() and dma_buf_put(), then falls
through to fastrpc_map_put() -> fastrpc_free_map().

Since map->table is still non-NULL, fastrpc_free_map() repeats the
cleanup: dma_buf_unmap_attachment_unlocked() dereferences the map->attach
already freed by dma_buf_detach() (use-after-free read), and a second
dma_buf_put() drops an extra reference on map->buf. As the exporting fd is
typically still held by userspace, this imbalance can later lead to
premature destruction of the dma_buf and a use-after-free.

The 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.

Clear map->table in the map_err path so the fastrpc_map_put() fallthrough
does not operate on the already released attachment and buffer.

Fixes: 334f1a1cbe03 ("misc: fastrpc: Use fastrpc_map_put in fastrpc_map_create on fail")
Cc: [email protected]
Assisted-by: Claude:claude-opus-4-8
Signed-off-by: Yifei Gao <[email protected]>
---
 drivers/misc/fastrpc.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/drivers/misc/fastrpc.c b/drivers/misc/fastrpc.c
index f3a49384586d..d6be951d5538 100644
--- a/drivers/misc/fastrpc.c
+++ b/drivers/misc/fastrpc.c
@@ -915,6 +915,7 @@ static int fastrpc_map_attach(struct fastrpc_user *fl, int fd,
 
 map_err:
 	dma_buf_detach(map->buf, map->attach);
+	map->table = NULL;
 attach_err:
 	dma_buf_put(map->buf);
 get_err:
-- 
2.43.0