On Tue, Aug 29, 2023 at 09:44:06PM +0500, Stas Sergeev wrote:

l3_len was calculated from the ethernet frame size, and it was assumed to be equal to the length stored in an IP packet. But if the ethernet frame is padded, then l3_len calculated that way can only be used as a bound check to validate the length stored in an IP header. It should not be used for calculating the l4_len.

This patch makes sure the small padded ethernet frames are properly processed, by trusting the length stored in an IP header.

Signed-off-by: Stas Sergeev

Reviewed-by: David Gibson

CC: Stefano Brivio --- tap.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/tap.c b/tap.c index ee79be0..8d7859c 100644 --- a/tap.c +++ b/tap.c @@ -615,7 +615,7 @@ resume: continue;

hlen = iph->ihl * 4UL; - if (hlen < sizeof(*iph) || htons(iph->tot_len) != l3_len || + if (hlen < sizeof(*iph) || htons(iph->tot_len) > l3_len || hlen > l3_len) continue;

@@ -623,7 +623,7 @@ resume: if (tap4_is_fragment(iph, now)) continue;

- l4_len = l3_len - hlen; + l4_len = htons(iph->tot_len) - hlen;

if (iph->saddr && c->ip4.addr_seen.s_addr != iph->saddr) c->ip4.addr_seen.s_addr = iph->saddr;

-- David Gibson | I'll have my music baroque, and my code david AT gibson.dropbear.id.au | minimalist, thank you. NOT _the_ _other_ | _way_ _around_! http://www.ozlabs.org/~dgibson