On 1/11/2019 2:30 PM, John Johansen wrote: > On 1/11/19 2:11 PM, Casey Schaufler wrote: >> On 1/11/2019 1:43 AM, syzbot wrote: >>> Hello, >>> >>> syzbot found the following crash on: >>> >>> HEAD commit: b808822a75a3 Add linux-next specific files for 20190111 >>> git tree: linux-next >>> console output: https://syzkaller.appspot.com/x/log.txt?x=179c22f7400000 >>> kernel config: https://syzkaller.appspot.com/x/.config?x=c052ead0aed5001b >>> dashboard link: https://syzkaller.appspot.com/bug?extid=69ca07954461f189e808 >>> compiler: gcc (GCC) 9.0.0 20181231 (experimental) >>> syz repro: https://syzkaller.appspot.com/x/repro.syz?x=162d947f400000 >>> C reproducer: https://syzkaller.appspot.com/x/repro.c?x=139f6c37400000 >>> >>> IMPORTANT: if you fix the bug, please add the following tag to the commit: >>> Reported-by: [email protected] >>> >>> ------------[ cut here ]------------ >>> AppArmor WARN cred_label: ((!blob)): >>> WARNING: CPU: 0 PID: 0 at security/apparmor/include/cred.h:30 cred_label >>> security/apparmor/include/cred.h:30 [inline] >>> WARNING: CPU: 0 PID: 0 at security/apparmor/include/cred.h:30 >>> apparmor_cred_free+0x12f/0x1a0 security/apparmor/lsm.c:62 >>> Kernel panic - not syncing: panic_on_warn set ... >>> CPU: 0 PID: 0 Comm: swapper/0 Not tainted 5.0.0-rc1-next-20190111 #10 >>> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS >>> Google 01/01/2011 >>> Call Trace: >>> <IRQ> >>> __dump_stack lib/dump_stack.c:77 [inline] >>> dump_stack+0x1db/0x2d0 lib/dump_stack.c:113 >>> panic+0x2cb/0x65c kernel/panic.c:214 >>> __warn.cold+0x20/0x48 kernel/panic.c:571 >>> report_bug+0x263/0x2b0 lib/bug.c:186 >>> fixup_bug arch/x86/kernel/traps.c:178 [inline] >>> fixup_bug arch/x86/kernel/traps.c:173 [inline] >>> do_error_trap+0x11b/0x200 arch/x86/kernel/traps.c:271 >>> do_invalid_op+0x37/0x50 arch/x86/kernel/traps.c:290 >>> invalid_op+0x14/0x20 arch/x86/entry/entry_64.S:973 >>> RIP: 0010:cred_label security/apparmor/include/cred.h:30 [inline] >>> RIP: 0010:apparmor_cred_free+0x12f/0x1a0 security/apparmor/lsm.c:62 >>> Code: 7c 88 48 c7 c7 00 d0 7c 88 e8 fd 70 f2 fd 0f 0b eb a9 e8 54 3f 29 fe >>> 48 c7 c6 c0 df 7c 88 48 c7 c7 00 d0 7c 88 e8 e1 70 f2 fd <0f> 0b 48 b8 00 >>> 00 00 00 00 fc ff df 80 38 00 75 4a 4c 8b 2c 25 00 >>> RSP: 0018:ffff8880ae6079f8 EFLAGS: 00010286 >>> RAX: 0000000000000000 RBX: 0000000000000000 RCX: 0000000000000000 >>> RDX: 0000000000000100 RSI: ffffffff81687fa6 RDI: 0000000000000006 >>> RBP: ffff8880ae607a18 R08: ffffffff8987dec0 R09: 0000000000000000 >>> R10: 0000000000000000 R11: 0000000000000000 R12: ffff8880a86b3100 >>> R13: ffff8880a86b3100 R14: ffff8880a86b3188 R15: dffffc0000000000 >>> security_cred_free+0x4b/0xf0 security/security.c:1490 >> The obvious thing to do is put a check in security_cred_free >> for a NULL cred->security, in which case the LSM hooks >> wouldn't get called. > Right, but the question is should we? To my thinking we shouldn't > ever have a cred without cred->security, unless the cred was > allocated but a later step in its construction, say allocating > ->security failed.
If allocating ->security fails in security_cred_alloc_blank() or security_prepare_creds() you don't have to do anything but fail because the LSM hooks are not called before the allocation. > In which case I'd rather see the cred directly freed and not > call into security_cred_free() as I like being able to detect > corrupt creds. I think we need to look for some bit of code that's setting cred->security to NULL inappropriately. > We certainly can still do the check for security on only live creds > but I would like to understand this particular failure better first > >> It's not clear to me how we got a cred >> that doesn't have an allocated security blob. > I have been trying to figure that one out as well. > > >>> put_cred_rcu+0x21f/0x6e0 kernel/cred.c:118 >>> __rcu_reclaim kernel/rcu/rcu.h:240 [inline] >>> rcu_do_batch kernel/rcu/tree.c:2486 [inline] >>> invoke_rcu_callbacks kernel/rcu/tree.c:2799 [inline] >>> rcu_core+0xc4a/0x1680 kernel/rcu/tree.c:2780 >>> __do_softirq+0x30b/0xb11 kernel/softirq.c:292 >>> invoke_softirq kernel/softirq.c:373 [inline] >>> irq_exit+0x180/0x1d0 kernel/softirq.c:413 >>> exiting_irq arch/x86/include/asm/apic.h:536 [inline] >>> smp_apic_timer_interrupt+0x1b7/0x760 arch/x86/kernel/apic/apic.c:1062 >>> apic_timer_interrupt+0xf/0x20 arch/x86/entry/entry_64.S:807 >>> </IRQ> >>> RIP: 0010:native_safe_halt+0x2/0x10 arch/x86/include/asm/irqflags.h:58 >>> Code: ff ff ff 48 89 c7 48 89 45 d8 e8 79 6f d0 f9 48 8b 45 d8 e9 ce fe ff >>> ff 48 89 df e8 68 6f d0 f9 eb 82 90 90 90 90 90 90 fb f4 <c3> 0f 1f 00 66 >>> 2e 0f 1f 84 00 00 00 00 00 f4 c3 90 90 90 90 90 90 >>> RSP: 0018:ffffffff89807c60 EFLAGS: 00000282 ORIG_RAX: ffffffffffffff13 >>> RAX: 1ffffffff1325061 RBX: 1ffffffff1300f8f RCX: 0000000000000000 >>> RDX: dffffc0000000000 RSI: 0000000000000001 RDI: ffffffff8987e73c >>> RBP: ffffffff89807d20 R08: ffffffff8987dec0 R09: 0000000000000000 >>> R10: 0000000000000000 R11: 0000000000000000 R12: 0000000000000000 >>> R13: ffffffff89807cf8 R14: 0000000000000000 R15: ffffffff899282f8 >>> arch_cpu_idle+0x10/0x20 arch/x86/kernel/process.c:555 >>> default_idle_call+0x36/0x90 kernel/sched/idle.c:93 >>> cpuidle_idle_call kernel/sched/idle.c:153 [inline] >>> do_idle+0x386/0x5d0 kernel/sched/idle.c:262 >>> cpu_startup_entry+0x1b/0x20 kernel/sched/idle.c:353 >>> rest_init+0x245/0x37b init/main.c:442 >>> arch_call_rest_init+0xe/0x1b >>> start_kernel+0x882/0x8bd init/main.c:742 >>> x86_64_start_reservations+0x29/0x2b arch/x86/kernel/head64.c:470 >>> x86_64_start_kernel+0x77/0x7b arch/x86/kernel/head64.c:451 >>> secondary_startup_64+0xa4/0xb0 arch/x86/kernel/head_64.S:243 >>> 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 [email protected]. >>> >>> syzbot will keep track of this bug report. See: >>> https://goo.gl/tpsmEJ#bug-status-tracking for how to communicate with >>> syzbot. >>> syzbot can test patches for this bug, for details see: >>> https://goo.gl/tpsmEJ#testing-patches >>> >
