[PATCH 4.20 45/65] 9p/net: put a lower bound on msize

From: Greg Kroah-Hartman
Date: Fri Jan 11 2019 - 09:46:21 EST


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

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

From: Dominique Martinet <dominique.martinet@xxxxxx>

commit 574d356b7a02c7e1b01a1d9cba8a26b3c2888f45 upstream.

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@xxxxxxxxxxxxx
Reported-by: syzbot+0c1d61e4db7db94102ca@xxxxxxxxxxxxxxxxxxxxxxxxx
Signed-off-by: Dominique Martinet <dominique.martinet@xxxxxx>
Cc: Eric Van Hensbergen <ericvh@xxxxxxxxx>
Cc: Latchesar Ionkov <lucho@xxxxxxxxxx>
Cc: stable@xxxxxxxxxxxxxxx
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

---
net/9p/client.c | 21 +++++++++++++++++++++
1 file changed, 21 insertions(+)

--- a/net/9p/client.c
+++ b/net/9p/client.c
@@ -181,6 +181,12 @@ static int parse_opts(char *opts, struct
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_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
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;