[PATCH v2] misc: fastrpc: Fix double free of 'buf' in error path

[Sukrut Bellary <sukrut.bellary@linux.com>]

smatch warning:
drivers/misc/fastrpc.c:1926 fastrpc_req_mmap() error: double free of 'buf'

In fastrpc_req_mmap() error path, the fastrpc buffer is freed in
fastrpc_req_munmap_impl() if unmap is successful.

But in the end, there is an unconditional call to fastrpc_buf_free().
So the above case triggers the double free of fastrpc buf.

Fixes: 72fa6f7820c4 ("misc: fastrpc: Rework fastrpc_req_munmap")
Reviewed-by: Shuah Khan <skhan@linuxfoundation.org>
Reviewed-by: Dan Carpenter <dan.carpenter@linaro.org>
Reviewed-by: Srinivas Kandagatla <srinivas.kandagatla@linaro.org>
Signed-off-by: Sukrut Bellary <sukrut.bellary@linux.com>
---
This is based on static analysis. Compilation tested.
---
Changes in v2: 
- Fixed the commit message.
- Addressed the review comment about deleting buf from the list
  before freeing.
- Link to v1: https://lore.kernel.org/all/20230518100829.515143-1-sukrut.bellary@linux.com/
---
 drivers/misc/fastrpc.c | 5 ++---
 1 file changed, 2 insertions(+), 3 deletions(-)

diff --git a/drivers/misc/fastrpc.c b/drivers/misc/fastrpc.c
index f48466960f1b..b3b520fcfb75 100644
--- a/drivers/misc/fastrpc.c
+++ b/drivers/misc/fastrpc.c
@@ -1882,7 +1882,8 @@ static int fastrpc_req_mmap(struct fastrpc_user *fl, char __user *argp)
 				      &args[0]);
 	if (err) {
 		dev_err(dev, "mmap error (len 0x%08llx)\n", buf->size);
-		goto err_invoke;
+		fastrpc_buf_free(buf);
+		return err;
 	}
 
 	/* update the buffer to be able to deallocate the memory on the DSP */
@@ -1922,8 +1923,6 @@ static int fastrpc_req_mmap(struct fastrpc_user *fl, char __user *argp)
 
 err_assign:
 	fastrpc_req_munmap_impl(fl, buf);
-err_invoke:
-	fastrpc_buf_free(buf);
 
 	return err;
 }
-- 
2.34.1