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AJvYcCXYn3s2gFBGHUPKfM7g8QqvBIvKinaNT545hwRXQDCzr/rFCw6IFqE+GSMxkNcnprDgFXY7D9AVu9OYQUdpr3onh0Om14KWXrCMG+Ij X-Gm-Message-State: AOJu0YzR/6afM/DqdRLmuAmd6gyhCQkG5pCaI+JrkLQlZ2rbHZpUsF6u /mRZ0mrv7b0qF7SaRSAwQXFnjkCx1FvWka7x2GLG+zF4PMWxsedmwehzVL9Zk3041RNAAFTrqKU lYoHIR3AEFSwZ6S+tQq3jeM/fxGSd9n8uddqk X-Received: by 2002:aa7:da8b:0:b0:568:7767:14fd with SMTP id q11-20020aa7da8b000000b00568776714fdmr659526eds.7.1711361144563; Mon, 25 Mar 2024 03:05:44 -0700 (PDT) Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 References: <20240324050554.1609460-1-syoshida@redhat.com> <20240325.183800.473265130872711273.syoshida@redhat.com> In-Reply-To: <20240325.183800.473265130872711273.syoshida@redhat.com> From: Eric Dumazet Date: Mon, 25 Mar 2024 11:05:33 +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 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_make_= skb() > >> tests HDRINCL to know if the skb has icmphdr. However, HDRINCL can cau= se a > >> race condition. If calling setsockopt(2) with IP_HDRINCL changes HDRIN= CL > >> 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 KMSA= N. > >> > >> Check FLOWI_FLAG_KNOWN_NH on fl4->flowi4_flags instead of testing HDRI= NCL > >> 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-gb3603fcb7= 9b1 #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_ou= tput.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 i= n __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 se= nd > >> 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_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 *f= l4) > { > 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) da= ta.