Messages in this thread | | | Date | Fri, 29 Mar 2024 17:02:47 +0900 (JST) | Subject | Re: [PATCH net] ipv4: Fix uninit-value access in __ip_make_skb() | From | Shigeru Yoshida <> |
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On Mon, 25 Mar 2024 20:56:43 +0100, Eric Dumazet wrote: > On Mon, Mar 25, 2024 at 6:46 PM Shigeru Yoshida <syoshida@redhat.com> wrote: >> >> On Mon, 25 Mar 2024 11:05:33 +0100, Eric Dumazet wrote: >> > On Mon, Mar 25, 2024 at 10:38 AM Shigeru Yoshida <syoshida@redhat.com> wrote: >> >> >> >> On Mon, 25 Mar 2024 10:01:25 +0100, Eric Dumazet wrote: >> >> > On Sun, Mar 24, 2024 at 6:06 AM Shigeru Yoshida <syoshida@redhat.com> wrote: >> >> >> >> >> >> KMSAN reported uninit-value access in __ip_make_skb() [1]. __ip_make_skb() >> >> >> tests HDRINCL to know if the skb has icmphdr. However, HDRINCL can cause a >> >> >> race condition. If calling setsockopt(2) with IP_HDRINCL changes HDRINCL >> >> >> while __ip_make_skb() is running, the function will access icmphdr in the >> >> >> skb even if it is not included. This causes the issue reported by KMSAN. >> >> >> >> >> >> Check FLOWI_FLAG_KNOWN_NH on fl4->flowi4_flags instead of testing HDRINCL >> >> >> on the socket. >> >> >> >> >> >> [1] >> >> > >> >> > What is the kernel version for this trace ? >> >> >> >> Sorry, I used the following version: >> >> >> >> CPU: 1 PID: 15709 Comm: syz-executor.7 Not tainted 6.8.0-11567-gb3603fcb79b1 #25 >> >> Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.16.3-1.fc39 04/01/2014 >> >> >> >> >> BUG: KMSAN: uninit-value in __ip_make_skb+0x2b74/0x2d20 net/ipv4/ip_output.c:1481 >> >> >> __ip_make_skb+0x2b74/0x2d20 net/ipv4/ip_output.c:1481 >> >> >> ip_finish_skb include/net/ip.h:243 [inline] >> >> >> ip_push_pending_frames+0x4c/0x5c0 net/ipv4/ip_output.c:1508 >> >> >> raw_sendmsg+0x2381/0x2690 net/ipv4/raw.c:654 >> >> >> inet_sendmsg+0x27b/0x2a0 net/ipv4/af_inet.c:851 >> >> >> sock_sendmsg_nosec net/socket.c:730 [inline] >> >> >> __sock_sendmsg+0x274/0x3c0 net/socket.c:745 >> >> >> __sys_sendto+0x62c/0x7b0 net/socket.c:2191 >> >> >> __do_sys_sendto net/socket.c:2203 [inline] >> >> >> __se_sys_sendto net/socket.c:2199 [inline] >> >> >> __x64_sys_sendto+0x130/0x200 net/socket.c:2199 >> >> >> do_syscall_64+0xd8/0x1f0 arch/x86/entry/common.c:83 >> >> >> entry_SYSCALL_64_after_hwframe+0x6d/0x75 >> >> >> >> >> >> Uninit was created at: >> >> >> slab_post_alloc_hook mm/slub.c:3804 [inline] >> >> >> slab_alloc_node mm/slub.c:3845 [inline] >> >> >> kmem_cache_alloc_node+0x5f6/0xc50 mm/slub.c:3888 >> >> >> kmalloc_reserve+0x13c/0x4a0 net/core/skbuff.c:577 >> >> >> __alloc_skb+0x35a/0x7c0 net/core/skbuff.c:668 >> >> >> alloc_skb include/linux/skbuff.h:1318 [inline] >> >> >> __ip_append_data+0x49ab/0x68c0 net/ipv4/ip_output.c:1128 >> >> >> ip_append_data+0x1e7/0x260 net/ipv4/ip_output.c:1365 >> >> >> raw_sendmsg+0x22b1/0x2690 net/ipv4/raw.c:648 >> >> >> inet_sendmsg+0x27b/0x2a0 net/ipv4/af_inet.c:851 >> >> >> sock_sendmsg_nosec net/socket.c:730 [inline] >> >> >> __sock_sendmsg+0x274/0x3c0 net/socket.c:745 >> >> >> __sys_sendto+0x62c/0x7b0 net/socket.c:2191 >> >> >> __do_sys_sendto net/socket.c:2203 [inline] >> >> >> __se_sys_sendto net/socket.c:2199 [inline] >> >> >> __x64_sys_sendto+0x130/0x200 net/socket.c:2199 >> >> >> do_syscall_64+0xd8/0x1f0 arch/x86/entry/common.c:83 >> >> >> entry_SYSCALL_64_after_hwframe+0x6d/0x75 >> >> >> >> >> >> Fixes: 99e5acae193e ("ipv4: Fix potential uninit variable access bug in __ip_make_skb()") >> >> >> Reported-by: syzkaller <syzkaller@googlegroups.com> >> >> >> Signed-off-by: Shigeru Yoshida <syoshida@redhat.com> >> >> >> --- >> >> >> I think IPv6 has a similar issue. If this patch is accepted, I will send >> >> >> a patch for IPv6. >> >> >> --- >> >> >> net/ipv4/ip_output.c | 2 +- >> >> >> 1 file changed, 1 insertion(+), 1 deletion(-) >> >> >> >> >> >> diff --git a/net/ipv4/ip_output.c b/net/ipv4/ip_output.c >> >> >> index 1fe794967211..39229fd0601a 100644 >> >> >> --- a/net/ipv4/ip_output.c >> >> >> +++ b/net/ipv4/ip_output.c >> >> >> @@ -1473,7 +1473,7 @@ struct sk_buff *__ip_make_skb(struct sock *sk, >> >> >> * by icmp_hdr(skb)->type. >> >> >> */ >> >> >> if (sk->sk_type == SOCK_RAW && >> >> >> - !inet_test_bit(HDRINCL, sk)) >> >> >> + !(fl4->flowi4_flags & FLOWI_FLAG_KNOWN_NH)) >> >> >> icmp_type = fl4->fl4_icmp_type; >> >> >> else >> >> >> icmp_type = icmp_hdr(skb)->type; >> >> >> -- >> >> >> 2.44.0 >> >> >> >> >> > >> >> > Thanks for your patch. >> >> > >> >> > I do not think this is enough, as far as syzkaller is concerned. >> >> > >> >> > raw_probe_proto_opt() can leave garbage in fl4_icmp_type (and fl4_icmp_code) >> >> >> >> Thank you for your comment. But I don't understand it clearly. What >> >> exactly do you mean by "garbage"? >> >> >> >> raw_probe_proto_opt() immediately returns 0 if fl4->flowi4_proto is >> >> not IPPROTO_ICMP: >> >> >> >> static int raw_probe_proto_opt(struct raw_frag_vec *rfv, struct flowi4 *fl4) >> >> { >> >> int err; >> >> >> >> if (fl4->flowi4_proto != IPPROTO_ICMP) >> >> return 0; >> >> >> >> In this case, the function doesn't set fl4_icmp_type. Do you mean this >> >> case? >> > >> > There are multiple ways to return early from this function. >> > >> > In all of them, fl4->fl4_icmp_type is left uninitialized, so syzbot >> > will find ways to trigger a related bug, >> > if you assume later that fl4->fl4_icmp_type contains valid (initialized) data. >> >> Thank you for your reply. I see your point. >> >> fl4->fl4_icmp_type is part of flowi_uli union in flowi4 structure, and >> flowi4_init_output() initializes fl4_dport and fl4_sport to zero. >> >> I thought this also initializes fl4_icmp_type and fl4_icmp_code. Do >> you think we should initialize fl4_icmp_type and fl4_icmp_code >> explicitly, otherwise am I misunderstanding? > > Yes, I am precisely saying this : do not rely on some union layout, > without mentioning it in the changelog > or even better in a comment. > > If you want to avoid clearing these fields, please add a > BUILD_BUG_ON() to make sure > a unrelated future change in include/net/flow.h does not break a > hidden assumption. > > (ie : clearing fl4_dport and fl4_sport also clears fl4_icmp_type and > fl4_icmp_code.)
Sorry for the late response.
Thank you Eric! I got it. I will try to make v2 patch this weekend.
Thanks, Shigeru
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