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 c69cee3feff0015d1a36800ad11c1a32bc2a4380..0b062959871fa6286b4dc5333d90822d0633f39c 100644 (file)
--- a/net/ipv4/esp4.c
+++ b/net/ipv4/esp4.c
@@ -921,7 +921,8 @@ 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 d674a24217f90fee2c7a4da4df85140a5159cbb1..68509e1f89b5b0f544f4c1b1747ef31e52b4adcb 100644 (file)
--- a/net/ipv4/ip_output.c
+++ b/net/ipv4/ip_output.c
@@ -1443,6 +1443,8 @@ 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 e87f3f8f068186525d76288142675685cbfb7293..0aaafc0bd8fa6a309eebb753ceb1c42129e790f7 100644 (file)
--- a/net/ipv6/esp6.c
+++ b/net/ipv6/esp6.c
@@ -968,7 +968,8 @@ 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++;