linux-kernel - [PATCH] misc: fastrpc: fix an incorrect NULL check on list iterator

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Date:   Sun, 27 Mar 2022 14:22:02 +0800
From:   Xiaomeng Tong <xiam0nd.tong@...il.com>
To:     srinivas.kandagatla@...aro.org
Cc:     amahesh@....qualcomm.com, arnd@...db.de,
        gregkh@...uxfoundation.org, jorge.ramirez-ortiz@...aro.org,
        linux-arm-msm@...r.kernel.org, linux-kernel@...r.kernel.org,
        Xiaomeng Tong <xiam0nd.tong@...il.com>, stable@...r.kernel.org
Subject: [PATCH] misc: fastrpc: fix an incorrect NULL check on list iterator

The bug is here:
	if (!buf) {

The list iterator value 'buf' will *always* be set and non-NULL
by list_for_each_entry(), so it is incorrect to assume that the
iterator value will be NULL if the list is empty (in this case, the
check 'if (!buf) {' will always be false and never exit expectly).

To fix the bug, use a new variable 'iter' as the list iterator,
while use the original variable 'buf' as a dedicated pointer to
point to the found element.

Cc: stable@...r.kernel.org
Fixes: 2419e55e532de ("misc: fastrpc: add mmap/unmap support")
Signed-off-by: Xiaomeng Tong <xiam0nd.tong@...il.com>
---
 drivers/misc/fastrpc.c | 9 +++++----
 1 file changed, 5 insertions(+), 4 deletions(-)

diff --git a/drivers/misc/fastrpc.c b/drivers/misc/fastrpc.c
index aa1682b94a23..45aaf54a7560 100644
--- a/drivers/misc/fastrpc.c
+++ b/drivers/misc/fastrpc.c
@@ -1353,17 +1353,18 @@ static int fastrpc_req_munmap_impl(struct fastrpc_user *fl,
 				   struct fastrpc_req_munmap *req)
 {
 	struct fastrpc_invoke_args args[1] = { [0] = { 0 } };
-	struct fastrpc_buf *buf, *b;
+	struct fastrpc_buf *buf = NULL, *iter, *b;
 	struct fastrpc_munmap_req_msg req_msg;
 	struct device *dev = fl->sctx->dev;
 	int err;
 	u32 sc;
 
 	spin_lock(&fl->lock);
-	list_for_each_entry_safe(buf, b, &fl->mmaps, node) {
-		if ((buf->raddr == req->vaddrout) && (buf->size == req->size))
+	list_for_each_entry_safe(iter, b, &fl->mmaps, node) {
+		if ((iter->raddr == req->vaddrout) && (iter->size == req->size)) {
+			buf = iter;
 			break;
-		buf = NULL;
+		}
 	}
 	spin_unlock(&fl->lock);
 
-- 
2.17.1