From 6c82c6098470fbd8098246b8268e06652446ac5b Mon Sep 17 00:00:00 2001 From: Jonathan Maple Date: Thu, 7 May 2026 15:40:36 -0400 Subject: [PATCH] xfrm: esp: avoid in-place decrypt on shared skb frags unpub-cve DIRTY-FRAG commit-author Kuan-Ting Chen commit f4c50a4034e62ab75f1d5cdd191dd5f9c77fdff4 upstream-diff | While this kernel lacks MSG_SPLICE_PAGES, it still has udp_sendpage(). Upstream didn't patch udp_sendpage() because sendpage was removed entirely in favor of MSG_SPLICE_PAGES. In this kernel, splice() can still attach a page cache page to an IPv4 datagram via sendpage. Therefore, udp_sendpage() must be patched instead. And there is no patch for IPv6 datagrams because it isn't affected; there's no sendpage callback for IPv6 UDP. MSG_SPLICE_PAGES can attach pages from a pipe directly to an skb. TCP marks such skbs with SKBFL_SHARED_FRAG after skb_splice_from_iter(), so later paths that may modify packet data can first make a private copy. The IPv4/IPv6 datagram append paths did not set this flag when splicing pages into UDP skbs. That leaves an ESP-in-UDP packet made from shared pipe pages looking like an ordinary uncloned nonlinear skb. ESP input then takes the no-COW fast path for uncloned skbs without a frag_list and decrypts in place over data that is not owned privately by the skb. Mark IPv4/IPv6 datagram splice frags with SKBFL_SHARED_FRAG, matching TCP. Also make ESP input fall back to skb_cow_data() when the flag is present, so ESP does not decrypt externally backed frags in place. Private nonlinear skb frags still use the existing fast path. This intentionally does not change ESP output. In esp_output_head(), the path that appends the ESP trailer to existing skb tailroom without calling skb_cow_data() is not reachable for nonlinear skbs: skb_tailroom() returns zero when skb->data_len is nonzero, while ESP tailen is positive. Thus ESP output will either use the separate destination-frag path or fall back to skb_cow_data(). Fixes: cac2661c53f3 ("esp4: Avoid skb_cow_data whenever possible") Fixes: 03e2a30f6a27 ("esp6: Avoid skb_cow_data whenever possible") Fixes: 7da0dde68486 ("ip, udp: Support MSG_SPLICE_PAGES") Fixes: 6d8192bd69bb ("ip6, udp6: Support MSG_SPLICE_PAGES") Reported-by: Hyunwoo Kim Reported-by: Kuan-Ting Chen Tested-by: Hyunwoo Kim Cc: stable@vger.kernel.org Signed-off-by: Kuan-Ting Chen Signed-off-by: Steffen Klassert (cherry picked from commit f4c50a4034e62ab75f1d5cdd191dd5f9c77fdff4) Signed-off-by: Jonathan Maple --- net/ipv4/esp4.c | 3 ++- net/ipv4/ip_output.c | 3 +++ 2 files changed, 5 insertions(+), 1 deletion(-) diff --git a/net/ipv4/esp4.c b/net/ipv4/esp4.c index 3f690c9705217..c17b357341a4b 100644 --- a/net/ipv4/esp4.c +++ b/net/ipv4/esp4.c @@ -920,7 +920,8 @@ static int esp_input(struct xfrm_state *x, struct sk_buff *skb) nfrags = 1; goto skip_cow; - } else if (!skb_has_frag_list(skb)) { + } else if (!skb_has_frag_list(skb) && + !skb_has_shared_frag(skb)) { nfrags = skb_shinfo(skb)->nr_frags; nfrags++; diff --git a/net/ipv4/ip_output.c b/net/ipv4/ip_output.c index dcabe4ea157bb..d61499a11d34e 100644 --- a/net/ipv4/ip_output.c +++ b/net/ipv4/ip_output.c @@ -1463,6 +1463,9 @@ ssize_t ip_append_page(struct sock *sk, struct flowi4 *fl4, struct page *page, goto error; } + if (!(flags & MSG_NO_SHARED_FRAGS)) + skb_shinfo(skb)->flags |= SKBFL_SHARED_FRAG; + if (skb->ip_summed == CHECKSUM_NONE) { __wsum csum; csum = csum_page(page, offset, len);