Commit 735ee858 authored by Florian Westphal's avatar Florian Westphal
Browse files

netfilter: xt_tcpmss: check remaining length before reading optlen 



Quoting reporter:
  In net/netfilter/xt_tcpmss.c (lines 53-68), the TCP option parser reads
 op[i+1] directly without validating the remaining option length.

  If the last byte of the option field is not EOL/NOP (0/1), the code attempts
  to index op[i+1]. In the case where i + 1 == optlen, this causes an
  out-of-bounds read, accessing memory past the optlen boundary
  (either reading beyond the stack buffer _opt or the
  following payload).

Reported-by: default avatarsungzii <sungzii@pm.me>
Signed-off-by: default avatarFlorian Westphal <fw@strlen.de>
parent de8a70ce

net/netfilter/xt_tcpmss.c

+1 −1
Original line number Diff line number Diff line
@@ -61,7 +61,7 @@ tcpmss_mt(const struct sk_buff *skb, struct xt_action_param *par) 
			return (mssval >= info->mss_min &&

				mssval <= info->mss_max) ^ info->invert;

		}

		if (op[i] < 2)

		if (op[i] < 2 || i == optlen - 1)

			i++;

		else

			i += op[i+1] ? : 1;