[PATCH 4.17 264/324] net/9p/client.c: put refcount of trans_mod in error case in parse_opts()

[Greg Kroah-Hartman]

4.17-stable review patch.  If anyone has any objections, please let me know.

------------------

From: piaojun <piaojun@xxxxxxxxxx>

[ Upstream commit c290fba8c4ce6530cd941ea14db5a4ac2f77183f ]

In my testing, the second mount will fail after umounting successfully.
The reason is that we put refcount of trans_mod in the correct case
rather than the error case in parse_opts() at last.  That will cause the
refcount decrease to -1, and when we try to get trans_mod again in
try_module_get(), we could only increase refcount to 0 which will cause
failure as follows:

parse_opts
  v9fs_get_trans_by_name
    try_module_get : return NULL to caller which cause error

So we should put refcount of trans_mod in error case.

Link: http://lkml.kernel.org/r/5B3F39A0.2030509@xxxxxxxxxx
Fixes: 9421c3e64137ec ("net/9p/client.c: fix potential refcnt problem of trans module")
Signed-off-by: Jun Piao <piaojun@xxxxxxxxxx>
Reviewed-by: Yiwen Jiang <jiangyiwen@xxxxxxxxxx>
Reviewed-by: Greg Kurz <groug@xxxxxxxx>
Reviewed-by: Dominique Martinet <dominique.martinet@xxxxxx>
Tested-by: Dominique Martinet <dominique.martinet@xxxxxx>
Cc: Eric Van Hensbergen <ericvh@xxxxxxxxx>
Cc: Ron Minnich <rminnich@xxxxxxxxxx>
Cc: Latchesar Ionkov <lucho@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Sasha Levin <alexander.levin@xxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
 net/9p/client.c |    3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

--- a/net/9p/client.c
+++ b/net/9p/client.c
@@ -228,7 +228,8 @@ static int parse_opts(char *opts, struct
 	}
 
 free_and_return:
-	v9fs_put_trans(clnt->trans_mod);
+	if (ret)
+		v9fs_put_trans(clnt->trans_mod);
 	kfree(tmp_options);
 	return ret;
 }