On 3/1/20 6:38 PM, Eric Dumazet wrote: > > > On 3/1/20 6:22 PM, Eric Dumazet wrote: >> >> >> On 3/1/20 5:33 PM, syzbot wrote: >>> Hello, >>> >>> syzbot found the following crash on: >>> >>> HEAD commit: fd786fb1 net: convert suitable drivers to use phy_do_ioctl.. >>> git tree: net-next >>> console output: https://syzkaller.appspot.com/x/log.txt?x=14e9726ee00000 >>> kernel config: https://syzkaller.appspot.com/x/.config?x=7f93900a7904130d >>> dashboard link: https://syzkaller.appspot.com/bug?extid=dd803bc0e8adf0003261 >>> compiler: gcc (GCC) 9.0.0 20181231 (experimental) >>> syz repro: https://syzkaller.appspot.com/x/repro.syz?x=12af9369e00000 >>> C reproducer: https://syzkaller.appspot.com/x/repro.c?x=10583d76e00000 >>> >>> The bug was bisected to: >>> >>> commit 14215108a1fd7e002c0a1f9faf8fbaf41fdda50d >>> Author: Cong Wang <xiyou.wangcong@xxxxxxxxx> >>> Date: Thu Feb 21 05:37:42 2019 +0000 >>> >>> net_sched: initialize net pointer inside tcf_exts_init() >>> >>> bisection log: https://syzkaller.appspot.com/x/bisect.txt?x=175b66bee00000 >>> final crash: https://syzkaller.appspot.com/x/report.txt?x=14db66bee00000 >>> console output: https://syzkaller.appspot.com/x/log.txt?x=10db66bee00000 >>> >>> IMPORTANT: if you fix the bug, please add the following tag to the commit: >>> Reported-by: syzbot+dd803bc0e8adf0003261@xxxxxxxxxxxxxxxxxxxxxxxxx >>> Fixes: 14215108a1fd ("net_sched: initialize net pointer inside tcf_exts_init()") >>> >>> RBP: 0000000000000000 R08: 0000000000000002 R09: 00000000bb1414ac >>> R10: 0000000000000000 R11: 0000000000000246 R12: ffffffffffffffff >>> R13: 0000000000000009 R14: 0000000000000000 R15: 0000000000000000 >>> ------------[ cut here ]------------ >>> refcount_t: underflow; use-after-free. >>> WARNING: CPU: 1 PID: 9577 at lib/refcount.c:28 refcount_warn_saturate+0x1dc/0x1f0 lib/refcount.c:28 >>> Kernel panic - not syncing: panic_on_warn set ... >>> CPU: 1 PID: 9577 Comm: syz-executor327 Not tainted 5.5.0-rc6-syzkaller #0 >>> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011 >>> Call Trace: >>> __dump_stack lib/dump_stack.c:77 [inline] >>> dump_stack+0x197/0x210 lib/dump_stack.c:118 >>> panic+0x2e3/0x75c kernel/panic.c:221 >>> __warn.cold+0x2f/0x3e kernel/panic.c:582 >>> report_bug+0x289/0x300 lib/bug.c:195 >>> fixup_bug arch/x86/kernel/traps.c:174 [inline] >>> fixup_bug arch/x86/kernel/traps.c:169 [inline] >>> do_error_trap+0x11b/0x200 arch/x86/kernel/traps.c:267 >>> do_invalid_op+0x37/0x50 arch/x86/kernel/traps.c:286 >>> invalid_op+0x23/0x30 arch/x86/entry/entry_64.S:1027 >>> RIP: 0010:refcount_warn_saturate+0x1dc/0x1f0 lib/refcount.c:28 >>> Code: e9 d8 fe ff ff 48 89 df e8 c1 f8 16 fe e9 85 fe ff ff e8 a7 77 d8 fd 48 c7 c7 e0 44 71 88 c6 05 9e 86 db 06 01 e8 93 27 a9 fd <0f> 0b e9 ac fe ff ff 0f 1f 00 66 2e 0f 1f 84 00 00 00 00 00 55 48 >>> RSP: 0018:ffffc9000c067b00 EFLAGS: 00010282 >>> RAX: 0000000000000000 RBX: 0000000000000000 RCX: 0000000000000000 >>> RDX: 0000000000000000 RSI: ffffffff815e5dd6 RDI: fffff5200180cf52 >>> RBP: ffffc9000c067b10 R08: ffff8880a8630340 R09: ffffed1015d26621 >>> R10: ffffed1015d26620 R11: ffff8880ae933107 R12: 0000000000000003 >>> R13: ffff888090256000 R14: ffff8880a7e5c040 R15: ffff8880a7e5c044 >>> refcount_sub_and_test include/linux/refcount.h:261 [inline] >>> refcount_dec_and_test include/linux/refcount.h:281 [inline] >>> put_net include/net/net_namespace.h:259 [inline] >>> __sk_destruct+0x6d8/0x7f0 net/core/sock.c:1723 >>> sk_destruct+0xd5/0x110 net/core/sock.c:1739 >>> __sk_free+0xfb/0x3f0 net/core/sock.c:1750 >>> sk_free+0x83/0xb0 net/core/sock.c:1761 >>> sock_put include/net/sock.h:1719 [inline] >>> __tun_detach+0xbe0/0x1150 drivers/net/tun.c:728 >>> tun_detach drivers/net/tun.c:740 [inline] >>> tun_chr_close+0xe0/0x180 drivers/net/tun.c:3455 >>> __fput+0x2ff/0x890 fs/file_table.c:280 >>> ____fput+0x16/0x20 fs/file_table.c:313 >>> task_work_run+0x145/0x1c0 kernel/task_work.c:113 >>> exit_task_work include/linux/task_work.h:22 [inline] >>> do_exit+0xba9/0x2f50 kernel/exit.c:801 >>> do_group_exit+0x135/0x360 kernel/exit.c:899 >>> __do_sys_exit_group kernel/exit.c:910 [inline] >>> __se_sys_exit_group kernel/exit.c:908 [inline] >>> __x64_sys_exit_group+0x44/0x50 kernel/exit.c:908 >>> do_syscall_64+0xfa/0x790 arch/x86/entry/common.c:294 >>> entry_SYSCALL_64_after_hwframe+0x49/0xbe >>> RIP: 0033:0x441a48 >>> Code: Bad RIP value. >>> RSP: 002b:00007fffe55809a8 EFLAGS: 00000246 ORIG_RAX: 00000000000000e7 >>> RAX: ffffffffffffffda RBX: 0000000000000001 RCX: 0000000000441a48 >>> RDX: 0000000000000001 RSI: 000000000000003c RDI: 0000000000000001 >>> RBP: 00000000004c8430 R08: 00000000000000e7 R09: ffffffffffffffd0 >>> R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000001 >>> R13: 00000000006dba80 R14: 0000000000000000 R15: 0000000000000000 >>> Kernel Offset: disabled >>> Rebooting in 86400 seconds.. >>> >>> >>> --- >>> This bug is generated by a bot. It may contain errors. >>> See https://goo.gl/tpsmEJ for more information about syzbot. >>> syzbot engineers can be reached at syzkaller@xxxxxxxxxxxxxxxx. >>> >>> syzbot will keep track of this bug report. See: >>> https://goo.gl/tpsmEJ#status for how to communicate with syzbot. >>> For information about bisection process see: https://goo.gl/tpsmEJ#bisection >>> syzbot can test patches for this bug, for details see: >>> https://goo.gl/tpsmEJ#testing-patches >>> >> >> >> Hmmm... maybe this patch would fix it ? >> >> diff --git a/include/net/pkt_cls.h b/include/net/pkt_cls.h >> index a972244ab1931a2fd52a41efa4f7a6cd78d8746a..6e258a6c1328e38a757d9711f4116a6672995b8f 100644 >> --- a/include/net/pkt_cls.h >> +++ b/include/net/pkt_cls.h >> @@ -206,11 +206,12 @@ static inline int tcf_exts_init(struct tcf_exts *exts, struct net *net, >> #ifdef CONFIG_NET_CLS_ACT >> exts->type = 0; >> exts->nr_actions = 0; >> - exts->net = net; >> + exts->net = NULL; >> exts->actions = kcalloc(TCA_ACT_MAX_PRIO, sizeof(struct tc_action *), >> GFP_KERNEL); >> if (!exts->actions) >> return -ENOMEM; >> + exts->net = net; >> #endif >> exts->action = action; >> exts->police = police; >> > > Hmm no. > > Instead, make sure cls_u32 gets a reference so that calls > to u32_destroy_key(new, false); do not end up decrementing netns refcount. > > > diff --git a/net/sched/cls_u32.c b/net/sched/cls_u32.c > index e15ff335953deef36e55901d8f4ce34e15ed676f..587d71def49157680cf54f84558c4f4e5dad37f1 100644 > --- a/net/sched/cls_u32.c > +++ b/net/sched/cls_u32.c > @@ -898,6 +898,7 @@ static int u32_change(struct net *net, struct sk_buff *in_skb, > new = u32_init_knode(net, tp, n); > if (!new) > return -ENOMEM; > + tcf_exts_get_net(&new->exts); > > err = u32_set_parms(net, tp, base, new, tb, > tca[TCA_RATE], ovr, extack); > @@ -918,7 +919,6 @@ static int u32_change(struct net *net, struct sk_buff *in_skb, > > u32_replace_knode(tp, tp_c, new); > tcf_unbind_filter(tp, &n->res); > - tcf_exts_get_net(&n->exts); > tcf_queue_work(&n->rwork, u32_delete_key_work); > return 0; > } > > Another possibility would be to have two different pointers to reduce possibility of a refcount mismatch in some complex error paths. tcf_exts_put_net() would have no effect if no prior call to tcf_exts_get_net() has been done. diff --git a/include/net/pkt_cls.h b/include/net/pkt_cls.h index a972244ab1931a2fd52a41efa4f7a6cd78d8746a..163caee65cd4ff07ce32699beab287ceffae0916 100644 --- a/include/net/pkt_cls.h +++ b/include/net/pkt_cls.h @@ -192,6 +192,7 @@ struct tcf_exts { int nr_actions; struct tc_action **actions; struct net *net; + struct net *ref_net; #endif /* Map to export classifier specific extension TLV types to the * generic extensions API. Unsupported extensions must be set to 0. @@ -207,6 +208,7 @@ static inline int tcf_exts_init(struct tcf_exts *exts, struct net *net, exts->type = 0; exts->nr_actions = 0; exts->net = net; + exts->ref_net = NULL; exts->actions = kcalloc(TCA_ACT_MAX_PRIO, sizeof(struct tc_action *), GFP_KERNEL); if (!exts->actions) @@ -224,8 +226,9 @@ static inline int tcf_exts_init(struct tcf_exts *exts, struct net *net, static inline bool tcf_exts_get_net(struct tcf_exts *exts) { #ifdef CONFIG_NET_CLS_ACT - exts->net = maybe_get_net(exts->net); - return exts->net != NULL; + WARN_ON_ONCE(exts->ref_net); + exts->ref_net = maybe_get_net(exts->net); + return exts->ref_net != NULL; #else return true; #endif @@ -234,8 +237,8 @@ static inline bool tcf_exts_get_net(struct tcf_exts *exts) static inline void tcf_exts_put_net(struct tcf_exts *exts) { #ifdef CONFIG_NET_CLS_ACT - if (exts->net) - put_net(exts->net); + if (exts->ref_net) + put_net(exts->ref_net); #endif }