On Wed, May 31, 2017 at 4:49 PM, Cong Wang <xiyou.wangc...@gmail.com> wrote: > On Wed, May 31, 2017 at 9:12 AM, Eric Dumazet <eric.duma...@gmail.com> wrote: >> On Wed, 2017-05-31 at 11:46 +0200, Andrey Konovalov wrote: >>> Hi, >>> >>> I've got the following error report while fuzzing the kernel with syzkaller. >>> >>> On commit 5ed02dbb497422bf225783f46e6eadd237d23d6b (4.12-rc3). >>> >>> Unfortunately it's not reproducible. >>> >>> ================================================================== >>> BUG: KASAN: use-after-free in add_grec+0x101e/0x1090 net/ipv4/igmp.c:473 >>> Read of size 8 at addr ffff88003053c1a0 by task swapper/0/0 >>> >>> CPU: 0 PID: 0 Comm: swapper/0 Not tainted 4.12.0-rc3+ #370 >>> Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Bochs 01/01/2011 >>> Call Trace: >>> <IRQ> >>> __dump_stack lib/dump_stack.c:16 [inline] >>> dump_stack+0x292/0x395 lib/dump_stack.c:52 >>> print_address_description+0x73/0x280 mm/kasan/report.c:252 >>> kasan_report_error mm/kasan/report.c:351 [inline] >>> kasan_report+0x22b/0x340 mm/kasan/report.c:408 >>> __asan_report_load8_noabort+0x14/0x20 mm/kasan/report.c:429 >>> add_grec+0x101e/0x1090 net/ipv4/igmp.c:473 >>> igmpv3_send_cr net/ipv4/igmp.c:663 [inline] >>> igmp_ifc_timer_expire+0x46d/0xa80 net/ipv4/igmp.c:768 >>> IPVS: length: 51 != 8 >>> call_timer_fn+0x23f/0x800 kernel/time/timer.c:1268 >>> expire_timers kernel/time/timer.c:1307 [inline] >>> __run_timers+0x94e/0xcd0 kernel/time/timer.c:1601 >>> run_timer_softirq+0x21/0x80 kernel/time/timer.c:1614 >>> __do_softirq+0x2fb/0xb99 kernel/softirq.c:284 >>> invoke_softirq kernel/softirq.c:364 [inline] >>> irq_exit+0x19e/0x1d0 kernel/softirq.c:405 >>> exiting_irq arch/x86/include/asm/apic.h:652 [inline] >>> smp_apic_timer_interrupt+0x76/0xa0 arch/x86/kernel/apic/apic.c:966 >>> apic_timer_interrupt+0x93/0xa0 arch/x86/entry/entry_64.S:481 >>> RIP: 0010:native_safe_halt+0x6/0x10 arch/x86/include/asm/irqflags.h:53 >>> RSP: 0018:ffffffff85a079a8 EFLAGS: 00000282 ORIG_RAX: ffffffffffffff10 >>> RAX: dffffc0000000020 RBX: 1ffffffff0b40f38 RCX: 0000000000000000 >>> RDX: 0000000000000000 RSI: 0000000000000001 RDI: ffffffff85a2a9e4 >>> RBP: ffffffff85a079a8 R08: 0000000000000000 R09: 0000000000000000 >>> R10: 0000000000000000 R11: 0000000000000000 R12: dffffc0000000000 >>> R13: ffffffff85a07a60 R14: ffffffff86171338 R15: 1ffffffff0b40f5b >>> </IRQ> >>> arch_safe_halt arch/x86/include/asm/paravirt.h:98 [inline] >>> default_idle+0x8f/0x440 arch/x86/kernel/process.c:341 >>> arch_cpu_idle+0xa/0x10 arch/x86/kernel/process.c:332 >>> default_idle_call+0x36/0x60 kernel/sched/idle.c:98 >>> cpuidle_idle_call kernel/sched/idle.c:156 [inline] >>> do_idle+0x348/0x420 kernel/sched/idle.c:245 >>> cpu_startup_entry+0x18/0x20 kernel/sched/idle.c:350 >>> rest_init+0x18d/0x1a0 init/main.c:415 >>> start_kernel+0x747/0x779 init/main.c:679 >>> x86_64_start_reservations+0x2a/0x2c arch/x86/kernel/head64.c:196 >>> x86_64_start_kernel+0x132/0x141 arch/x86/kernel/head64.c:177 >>> secondary_startup_64+0x9f/0x9f arch/x86/kernel/head_64.S:304 >>> >>> Allocated by task 30543: >>> save_stack_trace+0x16/0x20 arch/x86/kernel/stacktrace.c:59 >>> save_stack+0x43/0xd0 mm/kasan/kasan.c:513 >>> set_track mm/kasan/kasan.c:525 [inline] >>> kasan_kmalloc+0xad/0xe0 mm/kasan/kasan.c:617 >>> kmem_cache_alloc_trace+0x82/0x270 mm/slub.c:2745 >>> kmalloc include/linux/slab.h:492 [inline] >>> kzalloc include/linux/slab.h:665 [inline] >>> ip_mc_add1_src net/ipv4/igmp.c:1909 [inline] >>> ip_mc_add_src+0x6cd/0x1020 net/ipv4/igmp.c:2033 >>> ip_mc_msfilter+0x5e5/0xcf0 net/ipv4/igmp.c:2403 >>> do_ip_setsockopt.isra.12+0x2d47/0x38c0 net/ipv4/ip_sockglue.c:959 >>> ip_setsockopt+0x3a/0xb0 net/ipv4/ip_sockglue.c:1256 >>> tcp_setsockopt+0x82/0xd0 net/ipv4/tcp.c:2740 >>> sock_common_setsockopt+0x95/0xd0 net/core/sock.c:2844 >>> SYSC_setsockopt net/socket.c:1798 [inline] >>> SyS_setsockopt+0x270/0x3a0 net/socket.c:1777 >>> entry_SYSCALL_64_fastpath+0x1f/0xbe >>> >>> Freed by task 30543: >>> save_stack_trace+0x16/0x20 arch/x86/kernel/stacktrace.c:59 >>> save_stack+0x43/0xd0 mm/kasan/kasan.c:513 >>> set_track mm/kasan/kasan.c:525 [inline] >>> kasan_slab_free+0x72/0xc0 mm/kasan/kasan.c:590 >>> slab_free_hook mm/slub.c:1357 [inline] >>> slab_free_freelist_hook mm/slub.c:1379 [inline] >>> slab_free mm/slub.c:2961 [inline] >>> kfree+0xe8/0x2b0 mm/slub.c:3882 >>> ip_mc_clear_src+0x69/0x1c0 net/ipv4/igmp.c:2078 >>> ip_mc_dec_group+0x19a/0x470 net/ipv4/igmp.c:1618 >>> ip_mc_drop_socket+0x145/0x230 net/ipv4/igmp.c:2609 >>> inet_release+0x4e/0x1c0 net/ipv4/af_inet.c:411 >>> sock_release+0x8d/0x1e0 net/socket.c:597 >>> sock_close+0x16/0x20 net/socket.c:1072 >>> __fput+0x332/0x7f0 fs/file_table.c:209 >>> ____fput+0x15/0x20 fs/file_table.c:245 >>> task_work_run+0x19b/0x270 kernel/task_work.c:116 >>> exit_task_work include/linux/task_work.h:21 [inline] >>> do_exit+0x18a3/0x2820 kernel/exit.c:878 >>> do_group_exit+0x149/0x420 kernel/exit.c:982 >>> get_signal+0x76d/0x1790 kernel/signal.c:2318 >>> do_signal+0xd2/0x2130 arch/x86/kernel/signal.c:808 >>> exit_to_usermode_loop+0x17a/0x210 arch/x86/entry/common.c:157 >>> prepare_exit_to_usermode arch/x86/entry/common.c:194 [inline] >>> syscall_return_slowpath+0x3ba/0x410 arch/x86/entry/common.c:263 >>> entry_SYSCALL_64_fastpath+0xbc/0xbe >>> >>> The buggy address belongs to the object at ffff88003053c1a0 >>> which belongs to the cache kmalloc-64 of size 64 >>> The buggy address is located 0 bytes inside of >>> 64-byte region [ffff88003053c1a0, ffff88003053c1e0) >>> The buggy address belongs to the page: >>> page:ffffea0000c14f00 count:1 mapcount:0 mapping: (null) >>> index:0x0 compound_mapcount: 0 >>> flags: 0x100000000008100(slab|head) >>> raw: 0100000000008100 0000000000000000 0000000000000000 0000000100140014 >>> raw: ffffea0000c2f520 ffffea0000e20aa0 ffff88003e80f740 0000000000000000 >>> page dumped because: kasan: bad access detected >>> >>> Memory state around the buggy address: >>> ffff88003053c080: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc >>> ffff88003053c100: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc >>> >ffff88003053c180: fc fc fc fc fb fb fb fb fb fb fb fb fc fc fc fc >>> ^ >>> ffff88003053c200: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc >>> ffff88003053c280: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc >>> ================================================================== >> >> I have the feeling that ip_mc_clear_src() is called too soon. >> >> We should call it once all users have released their reference. > > In this case, ip_mc_clear_src() is called when the ->users hits > zero, therefore I think we possibly miss the refcnt on ->users. > > diff --git a/net/ipv4/igmp.c b/net/ipv4/igmp.c > index 44fd86d..c2f3347 100644 > --- a/net/ipv4/igmp.c > +++ b/net/ipv4/igmp.c > @@ -1886,6 +1886,7 @@ static int ip_mc_del_src(struct in_device > *in_dev, __be32 *pmca, int sfmode, > igmp_ifc_event(pmc->interface); > #endif > } > + pmc->users--; > out_unlock: > spin_unlock_bh(&pmc->lock); > return err; > @@ -2025,6 +2026,7 @@ static int ip_mc_add_src(struct in_device > *in_dev, __be32 *pmca, int sfmode, > #ifdef CONFIG_IP_MULTICAST > sf_markstate(pmc); > #endif > + pmc->users++; > isexclude = pmc->sfmode == MCAST_EXCLUDE; > if (!delta) > pmc->sfcount[sfmode]++;
The issue here is the timer firing while ip_mc_clear_src() has been already called. My patch should fix the problem. Or another one using del_timer_sync() instead of del_timer() in igmp_stop_timer(), but such a change would be more invasive, since the del_timer_sync() would need to happen while im->lock spinlock is not held.
