linux-kernel - [PATCH] misc: fastrpc: Fix double free of 'buf' in error path

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Message-Id: <20230518100829.515143-1-sukrut.bellary@linux.com>
Date:   Thu, 18 May 2023 03:08:29 -0700
From:   Sukrut Bellary <sukrut.bellary@...ux.com>
To:     Srinivas Kandagatla <srinivas.kandagatla@...aro.org>,
        Amol Maheshwari <amahesh@....qualcomm.com>,
        Arnd Bergmann <arnd@...db.de>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     Sukrut Bellary <sukrut.bellary@...ux.com>,
        linux-arm-msm@...r.kernel.org, linux-kernel@...r.kernel.org,
        kernel-janitors@...r.kernel.org,
        Shuah Khan <skhan@...uxfoundation.org>
Subject: [PATCH] misc: fastrpc: Fix double free of 'buf' in error path

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.

Fix this by avoiding the call to the second fastrpc_buf_free() if
fastrpc_req_munmap_impl() is successful.
'err' is not updated as it needs to retain the err returned by
qcom_scm_assign_mem(), which is the starting point of this error path.

This is based on static analysis only. Compilation tested.

Reviewed-by: Shuah Khan <skhan@...uxfoundation.org>
Signed-off-by: Sukrut Bellary <sukrut.bellary@...ux.com>
---
 drivers/misc/fastrpc.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/drivers/misc/fastrpc.c b/drivers/misc/fastrpc.c
index f48466960f1b..1c3ab78f274f 100644
--- a/drivers/misc/fastrpc.c
+++ b/drivers/misc/fastrpc.c
@@ -1921,7 +1921,10 @@ static int fastrpc_req_mmap(struct fastrpc_user *fl, char __user *argp)
 	return 0;
 
 err_assign:
-	fastrpc_req_munmap_impl(fl, buf);
+	if (!fastrpc_req_munmap_impl(fl, buf)) {
+		/* buf is freed */
+		return err;
+	}
 err_invoke:
 	fastrpc_buf_free(buf);
 
-- 
2.34.1