| Message ID | 20200813074611.281558-1-fw@strlen.de |
|---|---|
| State | New |
| Headers | show |
| Series | [nf] netfilter/ebtables: reject bogus getopt len value | expand |
diff --git a/net/bridge/netfilter/ebtables.c b/net/bridge/netfilter/ebtables.c index 1641f414d1ba..ebe33b60efd6 100644 --- a/net/bridge/netfilter/ebtables.c +++ b/net/bridge/netfilter/ebtables.c @@ -2238,6 +2238,10 @@ static int compat_do_ebt_get_ctl(struct sock *sk, int cmd, struct ebt_table *t; struct net *net = sock_net(sk); + if ((cmd == EBT_SO_GET_INFO || cmd == EBT_SO_GET_INIT_INFO) && + *len != sizeof(struct compat_ebt_replace)) + return -EINVAL; + if (copy_from_user(&tmp, user, sizeof(tmp))) return -EFAULT;
syzkaller reports splat: ------------[ cut here ]------------ Buffer overflow detected (80 < 137)! Call Trace: do_ebt_get_ctl+0x2b4/0x790 net/bridge/netfilter/ebtables.c:2317 nf_getsockopt+0x72/0xd0 net/netfilter/nf_sockopt.c:116 ip_getsockopt net/ipv4/ip_sockglue.c:1778 [inline] caused by a copy-to-user with a too-large "*len" value. This adds a argument check on *len just like in the non-compat version of the handler. Before the "Fixes" commit, the reproducer fails with -EINVAL as expected: 1. core calls the "compat" getsockopt version 2. compat getsockopt version detects the *len value is possibly in 64-bit layout (*len != compat_len) 3. compat getsockopt version delegates everything to native getsockopt version 4. native getsockopt rejects invalid *len -> compat handler only sees len == sizeof(compat_struct) for GET_ENTRIES. After the refactor, event sequence is: 1. getsockopt calls "compat" version (len != native_len) 2. compat version attempts to copy *len bytes, where *len is random value from userspace Fixes: fc66de8e16e ("netfilter/ebtables: clean up compat {get, set}sockopt handling") Reported-by: syzbot+5accb5c62faa1d346480@syzkaller.appspotmail.com Signed-off-by: Florian Westphal <fw@strlen.de> --- net/bridge/netfilter/ebtables.c | 4 ++++ 1 file changed, 4 insertions(+)