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AJvYcCVCJ0fFGWJWCtAophIqnwvt1EA73bPzK1QoiyUIbUeauSxGTmmmiX7riPo68iOhcxiXmafabc0zvTN4jbHj80oED4p/p7MPUcXc0ShL X-Gm-Message-State: AOJu0Yyys1ytOcRLl4u24TDoM4dylcGEiS9pfYz6HSJE6AcV3CcOJgRt Bw83AThxoKzTrGyu8AGJWfiIrL1ZoBGxZa7hPXP+ngfw7iT1AT11F6/lw8XAFZ3TguPfwkU04O6 Dbcbh6oH+46Yf+1gdqaRTcoZnHxR1eZCXRjPJ X-Received: by 2002:a05:6402:28a:b0:568:856b:f3c5 with SMTP id l10-20020a056402028a00b00568856bf3c5mr622edv.1.1711396617881; Mon, 25 Mar 2024 12:56:57 -0700 (PDT) Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 References: <20240325.183800.473265130872711273.syoshida@redhat.com> <20240326.024626.67077498140213947.syoshida@redhat.com> In-Reply-To: <20240326.024626.67077498140213947.syoshida@redhat.com> From: Eric Dumazet Date: Mon, 25 Mar 2024 20:56:43 +0100 Message-ID: Subject: Re: [PATCH net] ipv4: Fix uninit-value access in __ip_make_skb() To: Shigeru Yoshida Cc: davem@davemloft.net, dsahern@kernel.org, kuba@kernel.org, pabeni@redhat.com, netdev@vger.kernel.org, linux-kernel@vger.kernel.org, syzkaller@googlegroups.com Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable On Mon, Mar 25, 2024 at 6:46=E2=80=AFPM Shigeru Yoshida wrote: > > On Mon, 25 Mar 2024 11:05:33 +0100, Eric Dumazet wrote: > > On Mon, Mar 25, 2024 at 10:38=E2=80=AFAM Shigeru Yoshida wrote: > >> > >> On Mon, 25 Mar 2024 10:01:25 +0100, Eric Dumazet wrote: > >> > On Sun, Mar 24, 2024 at 6:06=E2=80=AFAM Shigeru Yoshida wrote: > >> >> > >> >> KMSAN reported uninit-value access in __ip_make_skb() [1]. __ip_ma= ke_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 HD= RINCL > >> >> 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 K= MSAN. > >> >> > >> >> Check FLOWI_FLAG_KNOWN_NH on fl4->flowi4_flags instead of testing H= DRINCL > >> >> 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-gb3603f= cb79b1 #25 > >> Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.16.3-1.f= c39 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 bu= g in __ip_make_skb()") > >> >> Reported-by: syzkaller > >> >> Signed-off-by: Shigeru Yoshida > >> >> --- > >> >> 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 =3D=3D SOCK_RAW && > >> >> - !inet_test_bit(HDRINCL, sk)) > >> >> + !(fl4->flowi4_flags & FLOWI_FLAG_KNOWN_NH)) > >> >> icmp_type =3D fl4->fl4_icmp_type; > >> >> else > >> >> icmp_type =3D 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_ic= mp_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 !=3D 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.)