xfrm: esp: avoid in-place decrypt on shared skb frags

commit f4c50a4034e62ab75f1d5cdd191dd5f9c77fdff4 upstream.

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 <imv4bel@gmail.com>
Reported-by: Kuan-Ting Chen <h3xrabbit@gmail.com>
Tested-by: Hyunwoo Kim <imv4bel@gmail.com>
Cc: stable@vger.kernel.org
Signed-off-by: Kuan-Ting Chen <h3xrabbit@gmail.com>
Signed-off-by: Steffen Klassert <steffen.klassert@secunet.com>
[bwh: Backported to 6.1: set the SKBFL_SHARED_FRAG flag in
 ip_append_page() instead of __ip{,6}_append_data()]
Signed-off-by: Ben Hutchings <benh@debian.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/net/ipv4/esp4.c b/net/ipv4/esp4.c
index 95575bf78d5c1717456cd0757362987b0d7a4fdd..5d59b5923e6bd66240016bfafee954db345de624 100644 (file)
--- a/net/ipv4/esp4.c
+++ b/net/ipv4/esp4.c
@@ -873,7 +873,8 @@ 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 79cf1385e8d24d5b0e6ff8da180c522182d16306..ec8279278deaebf99d36e0a36dbd37b49546408a 100644 (file)
--- a/net/ipv4/ip_output.c
+++ b/net/ipv4/ip_output.c
@@ -1463,6 +1463,8 @@ ssize_t   ip_append_page(struct sock *sk, struct flowi4 *fl4, struct page *page,
                        goto error;
                }
 
+               skb_shinfo(skb)->tx_flags |= SKBFL_SHARED_FRAG;
+
                if (skb->ip_summed == CHECKSUM_NONE) {
                        __wsum csum;
                        csum = csum_page(page, offset, len);

diff --git a/net/ipv6/esp6.c b/net/ipv6/esp6.c
index 76699ec8837026d0c5696887cb88e0c2ab72bde9..51de2d4f7a2fbacae00e5d0782d66f2b6c1d5e21 100644 (file)
--- a/net/ipv6/esp6.c
+++ b/net/ipv6/esp6.c
@@ -921,7 +921,8 @@ static int esp6_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++;