netfilter: xt_nfacct: don't assume acct name is null-terminated

BUG: KASAN: slab-out-of-bounds in .. lib/vsprintf.c:721
Read of size 1 at addr ffff88801eac95c8 by task syz-executor183/5851
[..]
 string+0x231/0x2b0 lib/vsprintf.c:721
 vsnprintf+0x739/0xf00 lib/vsprintf.c:2874
 [..]
 nfacct_mt_checkentry+0xd2/0xe0 net/netfilter/xt_nfacct.c:41
 xt_check_match+0x3d1/0xab0 net/netfilter/x_tables.c:523

nfnl_acct_find_get() handles non-null input, but the error
printk relied on its presence.

Reported-by: syzbot+4ff165b9251e4d295690@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=4ff165b9251e4d295690
Tested-by: syzbot+4ff165b9251e4d295690@syzkaller.appspotmail.com
Fixes: ceb98d03eac5 ("netfilter: xtables: add nfacct match to support extended accounting")
Signed-off-by: Florian Westphal <fw@strlen.de>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

diff --git a/net/netfilter/xt_nfacct.c b/net/netfilter/xt_nfacct.c
index 7c6bf1c168131a08ee0b79ae409214686e6f15a0..0ca1cdfc4095b60ca4deff75b4f6ebd004fd88b2 100644 (file)
--- a/net/netfilter/xt_nfacct.c
+++ b/net/netfilter/xt_nfacct.c
@@ -38,8 +38,8 @@ nfacct_mt_checkentry(const struct xt_mtchk_param *par)
 
        nfacct = nfnl_acct_find_get(par->net, info->name);
        if (nfacct == NULL) {
-               pr_info_ratelimited("accounting object `%s' does not exists\n",
-                                   info->name);
+               pr_info_ratelimited("accounting object `%.*s' does not exist\n",
+                                   NFACCT_NAME_MAX, info->name);
                return -ENOENT;
        }
        info->nfacct = nfacct;