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Commit 574d356b authored by Dominique Martinet's avatar Dominique Martinet
Browse files

9p/net: put a lower bound on msize 

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.

Link: http://lkml.kernel.org/r/1541407968-31350-1-git-send-email-asmadeus@codewreck.org


Reported-by: default avatar <syzbot+0c1d61e4db7db94102ca@syzkaller.appspotmail.com>
Signed-off-by: default avatarDominique Martinet <dominique.martinet@cea.fr>
Cc: Eric Van Hensbergen <ericvh@gmail.com>
Cc: Latchesar Ionkov <lucho@ionkov.net>
Cc: stable@vger.kernel.org
parent 52ad259e

net/9p/client.c

+21 −0
Original line number Diff line number Diff line
@@ -181,6 +181,12 @@ static int parse_opts(char *opts, struct p9_client *clnt) 
				ret = r;

				continue;

			}

			if (option < 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;