linux-kernel - [PATCH 4.9 14/83] 9p: clear dangling pointers in p9stat

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Date:   Mon, 19 Nov 2018 17:28:40 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org,
        Dominique Martinet <dominique.martinet@....fr>,
        syzbot+d4252148d198410b864f@...kaller.appspotmail.com,
        Sasha Levin <sashal@...nel.org>
Subject: [PATCH 4.9 14/83] 9p: clear dangling pointers in p9stat_free

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

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

From: Dominique Martinet <dominique.martinet@....fr>

[ 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@codewreck.org
Signed-off-by: Dominique Martinet <dominique.martinet@....fr>
Reported-by: syzbot+d4252148d198410b864f@...kaller.appspotmail.com
Signed-off-by: Sasha Levin <sashal@...nel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
 net/9p/protocol.c |    5 +++++
 1 file changed, 5 insertions(+)

--- a/net/9p/protocol.c
+++ b/net/9p/protocol.c
@@ -46,10 +46,15 @@ p9pdu_writef(struct p9_fcall *pdu, int p
 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);