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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: 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>
Cc: stable@vger.kernel.org
This commit is contained in:
Dominique Martinet 2018-11-05 09:52:48 +01:00
parent 52ad259eaa
commit 574d356b7a
1 changed files with 21 additions and 0 deletions
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21
net/9p/client.c
View File

@ -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;