Re: [PATCH net] filter: Account for tail adjustment during pull operations
From: Daniel Borkmann <daniel@iogearbox.net>
Date: 2022-12-13 22:43:05
Also in:
bpf
On 12/13/22 5:39 AM, Subash Abhinov Kasiviswanathan wrote:
quoted hunk ↗ jump to hunk
Extending the tail can have some unexpected side effects if a program is reading the content beyond the head skb headlen and all the skbs in the gso frag_list are linear with no head_frag - kernel BUG at net/core/skbuff.c:4219! pc : skb_segment+0xcf4/0xd2c lr : skb_segment+0x63c/0xd2c Call trace: skb_segment+0xcf4/0xd2c __udp_gso_segment+0xa4/0x544 udp4_ufo_fragment+0x184/0x1c0 inet_gso_segment+0x16c/0x3a4 skb_mac_gso_segment+0xd4/0x1b0 __skb_gso_segment+0xcc/0x12c udp_rcv_segment+0x54/0x16c udp_queue_rcv_skb+0x78/0x144 udp_unicast_rcv_skb+0x8c/0xa4 __udp4_lib_rcv+0x490/0x68c udp_rcv+0x20/0x30 ip_protocol_deliver_rcu+0x1b0/0x33c ip_local_deliver+0xd8/0x1f0 ip_rcv+0x98/0x1a4 deliver_ptype_list_skb+0x98/0x1ec __netif_receive_skb_core+0x978/0xc60 Fix this by marking these skbs as GSO_DODGY so segmentation can handle the tail updates accordingly. Fixes: 5293efe62df8 ("bpf: add bpf_skb_change_tail helper") Signed-off-by: Sean Tranchetti <redacted> Signed-off-by: Subash Abhinov Kasiviswanathan <redacted> --- net/core/filter.c | 14 ++++++++++++++ 1 file changed, 14 insertions(+)diff --git a/net/core/filter.c b/net/core/filter.c index bb0136e..d5f7f79 100644 --- a/net/core/filter.c +++ b/net/core/filter.c@@ -1654,6 +1654,20 @@ static DEFINE_PER_CPU(struct bpf_scratchpad, bpf_sp); static inline int __bpf_try_make_writable(struct sk_buff *skb, unsigned int write_len) { + struct sk_buff *list_skb = skb_shinfo(skb)->frag_list; + + if (skb_is_gso(skb) && list_skb && !list_skb->head_frag && + skb_headlen(list_skb)) { + int headlen = skb_headlen(skb); + int err = skb_ensure_writable(skb, write_len); + + /* pskb_pull_tail() has occurred */ + if (!err && headlen != skb_headlen(skb)) + skb_shinfo(skb)->gso_type |= SKB_GSO_DODGY; + + return err; + }
__bpf_try_make_writable() does not look like the right location to me given this is called also from various other places. bpf_skb_change_tail has skb_gso_reset in there, potentially that or pskb_pull_tail itself should mark it?
return skb_ensure_writable(skb, write_len); }