On 06/19/2016 03:24 AM, Alexander Potapenko wrote: > Hi Sasha, > > This commit delays the reuse of memory after it has been freed, so > it's intended to help people find more use-after-free errors. Is there a way to tell if the use-after-free access was to a memory that is quarantined? > But I'm puzzled why the stacks are missing. I looked at the logs, it looks like stackdepot ran out of room pretty early during boot. I've increased the max count and that solved the problem. Here's a trace with all the stacks: [ 1157.040216] BUG: KASAN: use-after-free in print_bad_pte+0x5c7/0x6e0 at addr ffff8801b82286a0 [ 1157.040222] Read of size 8 by task syz-executor/20583 [ 1157.040236] CPU: 0 PID: 20583 Comm: syz-executor Tainted: G B 4.7.0-rc2-next-20160609-sasha-00032-g779e0df-dirty #3123 [ 1157.040249] 1ffff10016b26e97 000000001af4d42c ffff8800b5937540 ffffffffa103380b [ 1157.040262] ffffffff00000000 fffffbfff5830bf4 0000000041b58ab3 ffffffffabaf1240 [ 1157.040274] ffffffffa103369c 0000000000000006 0000000000000000 ffff8800b5937550 [ 1157.040276] Call Trace: [ 1157.040290] [<ffffffffa103380b>] dump_stack+0x16f/0x1d4 [ 1157.040319] [<ffffffff9f7a148f>] kasan_report_error+0x59f/0x8c0 [ 1157.040382] [<ffffffff9f7a19c6>] __asan_report_load8_noabort+0x66/0x90 [ 1157.040409] [<ffffffff9f6fa5e7>] print_bad_pte+0x5c7/0x6e0 [ 1157.040418] [<ffffffff9f702e02>] unmap_page_range+0x12f2/0x1e20 [ 1157.040445] [<ffffffff9f703b69>] unmap_single_vma+0x239/0x250 [ 1157.040452] [<ffffffff9f7045e9>] unmap_vmas+0x119/0x1d0 [ 1157.040461] [<ffffffff9f720a73>] exit_mmap+0x2a3/0x410 [ 1157.040485] [<ffffffff9f3769e2>] mmput+0x192/0x350 [ 1157.040524] [<ffffffff9f38d745>] do_exit+0xea5/0x19e0 [ 1157.040566] [<ffffffff9f38e5d3>] do_group_exit+0x2e3/0x2f0 [ 1157.040580] [<ffffffff9f3b1928>] get_signal+0x1128/0x1370 [ 1157.040593] [<ffffffff9f1afca6>] do_signal+0x86/0x1da0 [ 1157.040700] [<ffffffff9f00539c>] exit_to_usermode_loop+0xac/0x200 [ 1157.040712] [<ffffffff9f006c20>] do_syscall_64+0x410/0x490 [ 1157.040725] [<ffffffffa94d0ca5>] entry_SYSCALL64_slow_path+0x25/0x25 [ 1157.040733] Object at ffff8801b8228600, in cache vm_area_struct [ 1157.040737] Object allocated with size 192 bytes. [ 1157.040738] Allocation: [ 1157.040741] PID = 20521 [ 1157.040757] [<ffffffff9f1dfae6>] save_stack_trace+0x26/0x70 [ 1157.040770] [<ffffffff9f7a01e6>] save_stack+0x46/0xd0 [ 1157.040784] [<ffffffff9f7a0470>] kasan_kmalloc+0x110/0x130 [ 1157.040797] [<ffffffff9f7a09a2>] kasan_slab_alloc+0x12/0x20 [ 1157.040811] [<ffffffff9f79a546>] kmem_cache_alloc+0x1e6/0x230 [ 1157.040826] [<ffffffff9f7245ad>] mmap_region+0x56d/0x13c0 [ 1157.040840] [<ffffffff9f725e22>] do_mmap+0xa22/0xaf0 [ 1157.040853] [<ffffffff9f6cb1af>] vm_mmap_pgoff+0x14f/0x1c0 [ 1157.040889] [<ffffffff9f71e5fb>] SyS_mmap_pgoff+0x81b/0x910 [ 1157.040901] [<ffffffff9f1bf966>] SyS_mmap+0x16/0x20 [ 1157.040910] [<ffffffff9f006ab6>] do_syscall_64+0x2a6/0x490 [ 1157.040919] [<ffffffffa94d0ca5>] return_from_SYSCALL_64+0x0/0x6a [ 1157.040920] Memory state around the buggy address: [ 1157.040927] ffff8801b8228580: fb fb fb fb fb fb fb fb fc fc fc fc fc fc fc fc [ 1157.040933] ffff8801b8228600: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb [ 1157.040938] >ffff8801b8228680: fb fb fb fb fb fb fb fb fc fc fc fc fc fc fc fc [ 1157.040940] ^ [ 1157.040946] ffff8801b8228700: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb [ 1157.040951] ffff8801b8228780: fb fb fb fb fb fb fb fb fc fc fc fc fc fc fc fc > Can you please share the reproduction steps for this bug? Just running syzkaller inside a kvmtool guest. > I also wonder whether it's reproducible when you: > - revert this commit? Not reproducible. > - build with SLAB instead of SLUB? Not reproducible. Thanks, Sasha -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>