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From: Dominique Martinet <asmadeus@codewreck.org>
To: unlisted-recipients:; (no To-header on input)
Cc: Dominique Martinet <dominique.martinet@cea.fr>,
	Eric Van Hensbergen <ericvh@gmail.com>,
	Latchesar Ionkov <lucho@ionkov.net>,
	syzkaller-bugs@googlegroups.com,
	v9fs-developer@lists.sourceforge.net,
	linux-kernel@vger.kernel.org, netdev@vger.kernel.org
Subject: [PATCH] 9p/net: put a lower bound on msize
Date: Mon,  5 Nov 2018 09:52:48 +0100
Message-ID: <1541407968-31350-1-git-send-email-asmadeus@codewreck.org> (raw)
In-Reply-To: <20181102223908.GA9565@nautica>

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

If the requested msize is too small (either from command line argument
or from the server version reply), we won't get any work done.
If it's *really* too small, nothing will work, and this got caught by
syzbot recently (on a new kmem_cache_create_usercopy() call)

Just set a minimum msize to 4k in both code paths, until someone
complains they have a use-case for a smaller msize.

We need to check in both mount option and server reply individually
because the msize for the first version request would be unchecked
with just a global check on clnt->msize.

Reported-by: syzbot+0c1d61e4db7db94102ca@syzkaller.appspotmail.com
Signed-off-by: Dominique Martinet <dominique.martinet@cea.fr>
Cc: Eric Van Hensbergen <ericvh@gmail.com>
Cc: Latchesar Ionkov <lucho@ionkov.net>
---
 net/9p/client.c | 21 +++++++++++++++++++++
 1 file changed, 21 insertions(+)

diff --git a/net/9p/client.c b/net/9p/client.c
index 2c9a17b9b46b..b1163ebdc622 100644
--- a/net/9p/client.c
+++ b/net/9p/client.c
@@ -181,6 +181,12 @@ static int parse_opts(char *opts, struct p9_client *clnt)
 				ret = r;
 				continue;
 			}
+			if (r < 4096) {
+				p9_debug(P9_DEBUG_ERROR,
+					 "msize should be at least 4k\n");
+				ret = -EINVAL;
+				continue;
+			}
 			clnt->msize = option;
 			break;
 		case Opt_trans:
@@ -983,10 +989,18 @@ static int p9_client_version(struct p9_client *c)
 	else if (!strncmp(version, "9P2000", 6))
 		c->proto_version = p9_proto_legacy;
 	else {
+		p9_debug(P9_DEBUG_ERROR,
+			 "server returned an unknown version: %s\n", version);
 		err = -EREMOTEIO;
 		goto error;
 	}
 
+	if (msize < 4096) {
+		p9_debug(P9_DEBUG_ERROR,
+			 "server returned a msize < 4096: %d\n", msize);
+		err = -EREMOTEIO;
+		goto error;
+	}
 	if (msize < c->msize)
 		c->msize = msize;
 
@@ -1043,6 +1057,13 @@ struct p9_client *p9_client_create(const char *dev_name, char *options)
 	if (clnt->msize > clnt->trans_mod->maxsize)
 		clnt->msize = clnt->trans_mod->maxsize;
 
+	if (clnt->msize < 4096) {
+		p9_debug(P9_DEBUG_ERROR,
+			 "Please specify a msize of at least 4k\n");
+		err = -EINVAL;
+		goto free_client;
+	}
+
 	err = p9_client_version(clnt);
 	if (err)
 		goto close_trans;
-- 
2.19.1


  reply index

Thread overview: 5+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-11-02 15:37 WARNING in kmem_cache_create_usercopy syzbot
2018-11-02 22:39 ` Dominique Martinet
2018-11-05  8:52   ` Dominique Martinet [this message]
2018-11-20  6:03     ` [PATCH] 9p/net: put a lower bound on msize Dominique Martinet
2018-11-07  2:29   ` WARNING in kmem_cache_create_usercopy Dmitry Vyukov

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