[PATCH AUTOSEL 4.19 55/57] 9p: clear dangling pointers in p9stat_free

[Sasha Levin]

From: Dominique Martinet <dominique.martinet@xxxxxx>

[ Upstream commit 62e3941776fea8678bb8120607039410b1b61a65 ]

p9stat_free is more of a cleanup function than a 'free' function as it
only frees the content of the struct; there are chances of use-after-free
if it is improperly used (e.g. p9stat_free called twice as it used to be
possible to)

Clearing dangling pointers makes the function idempotent and safer to use.

Link: http://lkml.kernel.org/r/1535410108-20650-2-git-send-email-asmadeus@xxxxxxxxxxxxx
Signed-off-by: Dominique Martinet <dominique.martinet@xxxxxx>
Reported-by: syzbot+d4252148d198410b864f@xxxxxxxxxxxxxxxxxxxxxxxxx
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
---
 net/9p/protocol.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/net/9p/protocol.c b/net/9p/protocol.c
index 4a1e1dd30b52..ee32bbf12675 100644
--- a/net/9p/protocol.c
+++ b/net/9p/protocol.c
@@ -46,10 +46,15 @@ p9pdu_writef(struct p9_fcall *pdu, int proto_version, const char *fmt, ...);
 void p9stat_free(struct p9_wstat *stbuf)
 {
 	kfree(stbuf->name);
+	stbuf->name = NULL;
 	kfree(stbuf->uid);
+	stbuf->uid = NULL;
 	kfree(stbuf->gid);
+	stbuf->gid = NULL;
 	kfree(stbuf->muid);
+	stbuf->muid = NULL;
 	kfree(stbuf->extension);
+	stbuf->extension = NULL;
 }
 EXPORT_SYMBOL(p9stat_free);
 
-- 
2.17.1