misc: fastrpc: fix an incorrect NULL check on list iterator

[ Upstream commit 5ac11fe03a0a83042d1a040dbce4fa2fb5521e23 ]

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.

Fixes: 2419e55e532de ("misc: fastrpc: add mmap/unmap support")
Signed-off-by: Xiaomeng Tong <xiam0nd.tong@gmail.com>
Link: https://lore.kernel.org/r/20220327062202.5720-1-xiam0nd.tong@gmail.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>

diff --git a/drivers/misc/fastrpc.c b/drivers/misc/fastrpc.c
index 86d8fb8..c7134d2 100644 (file)
--- a/drivers/misc/fastrpc.c
+++ b/drivers/misc/fastrpc.c
@@ -1351,17 +1351,18 @@ 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);