This is a note to let you know that I've just added the patch titled ipv4: fix ip option filtering for locally generated fragments to the 5.15-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary The filename of the patch is: ipv4-fix-ip-option-filtering-for-locally-generated-f.patch and it can be found in the queue-5.15 subdirectory. If you, or anyone else, feels it should not be added to the stable tree, please let <stable@xxxxxxxxxxxxxxx> know about it. commit ce72db6d15ce9ab3779c815b35f339a5a0f58003 Author: Jakub Kicinski <kuba@xxxxxxxxxx> Date: Fri Jan 21 16:57:31 2022 -0800 ipv4: fix ip option filtering for locally generated fragments [ Upstream commit 27a8caa59babb96c5890569e131bc0eb6d45daee ] During IP fragmentation we sanitize IP options. This means overwriting options which should not be copied with NOPs. Only the first fragment has the original, full options. ip_fraglist_prepare() copies the IP header and options from previous fragment to the next one. Commit 19c3401a917b ("net: ipv4: place control buffer handling away from fragmentation iterators") moved sanitizing options before ip_fraglist_prepare() which means options are sanitized and then overwritten again with the old values. Fixing this is not enough, however, nor did the sanitization work prior to aforementioned commit. ip_options_fragment() (which does the sanitization) uses ipcb->opt.optlen for the length of the options. ipcb->opt of fragments is not populated (it's 0), only the head skb has the state properly built. So even when called at the right time ip_options_fragment() does nothing. This seems to date back all the way to v2.5.44 when the fast path for pre-fragmented skbs had been introduced. Prior to that ip_options_build() would have been called for every fragment (in fact ever since v2.5.44 the fragmentation handing in ip_options_build() has been dead code, I'll clean it up in -next). In the original patch (see Link) caixf mentions fixing the handling for fragments other than the second one, but I'm not sure how _any_ fragment could have had their options sanitized with the code as it stood. Tested with python (MTU on lo lowered to 1000 to force fragmentation): import socket s = socket.socket(socket.AF_INET, socket.SOCK_DGRAM) s.setsockopt(socket.IPPROTO_IP, socket.IP_OPTIONS, bytearray([7,4,5,192, 20|0x80,4,1,0])) s.sendto(b'1'*2000, ('127.0.0.1', 1234)) Before: IP (tos 0x0, ttl 64, id 1053, offset 0, flags [+], proto UDP (17), length 996, options (RR [bad length 4] [bad ptr 5] 192.148.4.1,,RA value 256)) localhost.36500 > localhost.search-agent: UDP, length 2000 IP (tos 0x0, ttl 64, id 1053, offset 968, flags [+], proto UDP (17), length 996, options (RR [bad length 4] [bad ptr 5] 192.148.4.1,,RA value 256)) localhost > localhost: udp IP (tos 0x0, ttl 64, id 1053, offset 1936, flags [none], proto UDP (17), length 100, options (RR [bad length 4] [bad ptr 5] 192.148.4.1,,RA value 256)) localhost > localhost: udp After: IP (tos 0x0, ttl 96, id 42549, offset 0, flags [+], proto UDP (17), length 996, options (RR [bad length 4] [bad ptr 5] 192.148.4.1,,RA value 256)) localhost.51607 > localhost.search-agent: UDP, bad length 2000 > 960 IP (tos 0x0, ttl 96, id 42549, offset 968, flags [+], proto UDP (17), length 996, options (NOP,NOP,NOP,NOP,RA value 256)) localhost > localhost: udp IP (tos 0x0, ttl 96, id 42549, offset 1936, flags [none], proto UDP (17), length 100, options (NOP,NOP,NOP,NOP,RA value 256)) localhost > localhost: udp RA (20 | 0x80) is now copied as expected, RR (7) is "NOPed out". Link: https://lore.kernel.org/netdev/20220107080559.122713-1-ooppublic@xxxxxxx/ Fixes: 19c3401a917b ("net: ipv4: place control buffer handling away from fragmentation iterators") Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2") Signed-off-by: caixf <ooppublic@xxxxxxx> Signed-off-by: Jakub Kicinski <kuba@xxxxxxxxxx> Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx> Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx> diff --git a/net/ipv4/ip_output.c b/net/ipv4/ip_output.c index 9bca57ef8b838..ff38b46bd4b0f 100644 --- a/net/ipv4/ip_output.c +++ b/net/ipv4/ip_output.c @@ -826,15 +826,24 @@ int ip_do_fragment(struct net *net, struct sock *sk, struct sk_buff *skb, /* Everything is OK. Generate! */ ip_fraglist_init(skb, iph, hlen, &iter); - if (iter.frag) - ip_options_fragment(iter.frag); - for (;;) { /* Prepare header of the next frame, * before previous one went down. */ if (iter.frag) { + bool first_frag = (iter.offset == 0); + IPCB(iter.frag)->flags = IPCB(skb)->flags; ip_fraglist_prepare(skb, &iter); + if (first_frag && IPCB(skb)->opt.optlen) { + /* ipcb->opt is not populated for frags + * coming from __ip_make_skb(), + * ip_options_fragment() needs optlen + */ + IPCB(iter.frag)->opt.optlen = + IPCB(skb)->opt.optlen; + ip_options_fragment(iter.frag); + ip_send_check(iter.iph); + } } skb->tstamp = tstamp;