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([2620:15c:2c1:200:55c7:81e6:c7d8:94b]) by smtp.gmail.com with ESMTPSA id c14-v6sm790139lfi.23.2018.09.13.09.35.50 (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Thu, 13 Sep 2018 09:35:52 -0700 (PDT) Subject: Re: KMSAN: uninit-value in pppoe_rcv To: Alexander Potapenko , Eric Dumazet Cc: syzbot+f5f6080811c849739212@syzkaller.appspotmail.com, LKML , mostrows@earthlink.net, Networking , syzkaller-bugs@googlegroups.com References: <0000000000004624c30575a9fd40@google.com> <7424e094-afda-084a-ad80-299f219ced92@gmail.com> From: Eric Dumazet Message-ID: <315231c0-462e-45d4-aeab-3d546387e2ca@gmail.com> Date: Thu, 13 Sep 2018 09:35:48 -0700 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.6.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 09/13/2018 07:12 AM, Alexander Potapenko wrote: > On Thu, Sep 13, 2018 at 3:57 PM Eric Dumazet wrote: >> >> >> >> On 09/12/2018 03:38 AM, Alexander Potapenko wrote: >>> On Wed, Sep 12, 2018 at 12:24 PM syzbot >>> wrote: >>>> >>>> Hello, >>>> >>>> syzbot found the following crash on: >>>> >>>> HEAD commit: d2d741e5d189 kmsan: add initialization for shmem pages >>>> git tree: https://github.com/google/kmsan.git/master >>>> console output: https://syzkaller.appspot.com/x/log.txt?x=1465fc37800000 >>>> kernel config: https://syzkaller.appspot.com/x/.config?x=48f9de3384bcd0f >>>> dashboard link: https://syzkaller.appspot.com/bug?extid=f5f6080811c849739212 >>>> compiler: clang version 7.0.0 (trunk 329391) >>>> syz repro: https://syzkaller.appspot.com/x/repro.syz?x=14d6e607800000 >>>> C reproducer: https://syzkaller.appspot.com/x/repro.c?x=10a15b5b800000 >>>> >>>> IMPORTANT: if you fix the bug, please add the following tag to the commit: >>>> Reported-by: syzbot+f5f6080811c849739212@syzkaller.appspotmail.com >>>> >>>> IPVS: ftp: loaded support on port[0] = 21 >>>> ================================================================== >>>> BUG: KMSAN: uninit-value in __get_item drivers/net/ppp/pppoe.c:172 [inline] >>>> BUG: KMSAN: uninit-value in get_item drivers/net/ppp/pppoe.c:236 [inline] >>>> BUG: KMSAN: uninit-value in pppoe_rcv+0xcef/0x10e0 >>>> drivers/net/ppp/pppoe.c:450 >>>> CPU: 0 PID: 4543 Comm: syz-executor355 Not tainted 4.16.0+ #87 >>>> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS >>>> Google 01/01/2011 >>>> Call Trace: >>>> __dump_stack lib/dump_stack.c:17 [inline] >>>> dump_stack+0x185/0x1d0 lib/dump_stack.c:53 >>>> kmsan_report+0x142/0x240 mm/kmsan/kmsan.c:1067 >>>> __msan_warning_32+0x6c/0xb0 mm/kmsan/kmsan_instr.c:683 >>>> __get_item drivers/net/ppp/pppoe.c:172 [inline] >>>> get_item drivers/net/ppp/pppoe.c:236 [inline] >>>> pppoe_rcv+0xcef/0x10e0 drivers/net/ppp/pppoe.c:450 >>>> __netif_receive_skb_core+0x47df/0x4a90 net/core/dev.c:4562 >>>> __netif_receive_skb net/core/dev.c:4627 [inline] >>>> netif_receive_skb_internal+0x49d/0x630 net/core/dev.c:4701 >>>> netif_receive_skb+0x230/0x240 net/core/dev.c:4725 >>>> tun_rx_batched drivers/net/tun.c:1555 [inline] >>>> tun_get_user+0x740f/0x7c60 drivers/net/tun.c:1962 >>>> tun_chr_write_iter+0x1d4/0x330 drivers/net/tun.c:1990 >>>> call_write_iter include/linux/fs.h:1782 [inline] >>>> new_sync_write fs/read_write.c:469 [inline] >>>> __vfs_write+0x7fb/0x9f0 fs/read_write.c:482 >>>> vfs_write+0x463/0x8d0 fs/read_write.c:544 >>>> SYSC_write+0x172/0x360 fs/read_write.c:589 >>>> SyS_write+0x55/0x80 fs/read_write.c:581 >>>> do_syscall_64+0x309/0x430 arch/x86/entry/common.c:287 >>>> entry_SYSCALL_64_after_hwframe+0x3d/0xa2 >>>> RIP: 0033:0x4447c9 >>>> RSP: 002b:00007fff64c8fc28 EFLAGS: 00000297 ORIG_RAX: 0000000000000001 >>>> RAX: ffffffffffffffda RBX: 0000000000000000 RCX: 00000000004447c9 >>>> RDX: 000000000000fd87 RSI: 0000000020000600 RDI: 0000000000000004 >>>> RBP: 00000000006cf018 R08: 00007fff64c8fda8 R09: 00007fff00006bda >>>> R10: 0000000000005fe7 R11: 0000000000000297 R12: 00000000004020d0 >>>> R13: 0000000000402160 R14: 0000000000000000 R15: 0000000000000000 >>>> >>>> Uninit was created at: >>>> kmsan_save_stack_with_flags mm/kmsan/kmsan.c:278 [inline] >>>> kmsan_internal_poison_shadow+0xb8/0x1b0 mm/kmsan/kmsan.c:188 >>>> kmsan_kmalloc+0x94/0x100 mm/kmsan/kmsan.c:314 >>>> kmsan_slab_alloc+0x11/0x20 mm/kmsan/kmsan.c:321 >>>> slab_post_alloc_hook mm/slab.h:445 [inline] >>>> slab_alloc_node mm/slub.c:2737 [inline] >>>> __kmalloc_node_track_caller+0xaed/0x11c0 mm/slub.c:4369 >>>> __kmalloc_reserve net/core/skbuff.c:138 [inline] >>>> __alloc_skb+0x2cf/0x9f0 net/core/skbuff.c:206 >>>> alloc_skb include/linux/skbuff.h:984 [inline] >>>> alloc_skb_with_frags+0x1d4/0xb20 net/core/skbuff.c:5234 >>>> sock_alloc_send_pskb+0xb56/0x1190 net/core/sock.c:2085 >>>> tun_alloc_skb drivers/net/tun.c:1532 [inline] >>>> tun_get_user+0x2242/0x7c60 drivers/net/tun.c:1829 >>>> tun_chr_write_iter+0x1d4/0x330 drivers/net/tun.c:1990 >>>> call_write_iter include/linux/fs.h:1782 [inline] >>>> new_sync_write fs/read_write.c:469 [inline] >>>> __vfs_write+0x7fb/0x9f0 fs/read_write.c:482 >>>> vfs_write+0x463/0x8d0 fs/read_write.c:544 >>>> SYSC_write+0x172/0x360 fs/read_write.c:589 >>>> SyS_write+0x55/0x80 fs/read_write.c:581 >>>> do_syscall_64+0x309/0x430 arch/x86/entry/common.c:287 >>>> entry_SYSCALL_64_after_hwframe+0x3d/0xa2 >>>> ================================================================== >>> I did a little digging before sending the bug upstream. >>> If I add memset(obj, 0xfe, size) to __kmalloc_reserve(), these 0xfe >>> bytes are visible in __get_item() at the place where KMSAN reports an >>> error. >>> >>> The problem is somehow related to tun_get_user() creating a fragmented >>> sk_buff - when I change the call to tun_alloc_skb() so that it >>> allocates a single buffer the bug goes away. >>> >> >> I guess the following patch would fix the issue >> >> (I will submit it more formally) > No, as far as I can see it doesn't. > Saving sid before __skb_pull() is still a good idea, but in this > particular case |ph| doesn't change. >> diff --git a/drivers/net/ppp/pppoe.c b/drivers/net/ppp/pppoe.c >> index ce61231e96ea5fe27f512fbd0d80d4609997e508..333e967ed968ea3ff2dda25289f7f657263db2b9 100644 >> --- a/drivers/net/ppp/pppoe.c >> +++ b/drivers/net/ppp/pppoe.c >> @@ -423,6 +423,7 @@ static int pppoe_rcv(struct sk_buff *skb, struct net_device *dev, >> struct pppoe_hdr *ph; >> struct pppox_sock *po; >> struct pppoe_net *pn; >> + __be16 sid; >> int len; >> >> skb = skb_share_check(skb, GFP_ATOMIC); >> @@ -434,6 +435,7 @@ static int pppoe_rcv(struct sk_buff *skb, struct net_device *dev, >> >> ph = pppoe_hdr(skb); >> len = ntohs(ph->length); Then ph->length needs to be better validated. >> + sid = ph->sid; I'll take a look, thanks.