On Wed, Jan 02 2019, Jeff Layton wrote: > On Wed, 2019-01-02 at 02:31 -0800, syzbot wrote: >> Hello, >> >> syzbot found the following crash on: >> >> HEAD commit: e1ef035d272e Merge tag 'armsoc-defconfig' of git://git.ker.. >> git tree: upstream >> console output: https://syzkaller.appspot.com/x/log.txt?x=16bb4c4b400000 >> kernel config: https://syzkaller.appspot.com/x/.config?x=9c6a26e22579190b >> dashboard link: https://syzkaller.appspot.com/bug?extid=239d99847eb49ecb3899 >> compiler: gcc (GCC) 9.0.0 20181231 (experimental) >> syz repro: https://syzkaller.appspot.com/x/repro.syz?x=128aa377400000 >> >> IMPORTANT: if you fix the bug, please add the following tag to the commit: >> Reported-by: syzbot+239d99847eb49ecb3899@xxxxxxxxxxxxxxxxxxxxxxxxx >> >> IPv6: ADDRCONF(NETDEV_UP): vxcan1: link is not ready >> IPv6: ADDRCONF(NETDEV_UP): vxcan1: link is not ready >> 8021q: adding VLAN 0 to HW filter on device batadv0 >> 8021q: adding VLAN 0 to HW filter on device batadv0 >> ================================================================== >> BUG: KASAN: use-after-free in what_owner_is_waiting_for fs/locks.c:1000 >> [inline] >> BUG: KASAN: use-after-free in posix_locks_deadlock fs/locks.c:1023 [inline] >> BUG: KASAN: use-after-free in posix_lock_inode+0x1f9e/0x2750 fs/locks.c:1163 >> Read of size 8 at addr ffff88808791b000 by task syz-executor2/10100 >> >> CPU: 1 PID: 10100 Comm: syz-executor2 Not tainted 4.20.0+ #3 >> 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+0x1db/0x2d0 lib/dump_stack.c:113 >> print_address_description.cold+0x7c/0x20d mm/kasan/report.c:187 >> kasan_report.cold+0x1b/0x40 mm/kasan/report.c:317 >> __asan_report_load8_noabort+0x14/0x20 mm/kasan/generic_report.c:135 >> what_owner_is_waiting_for fs/locks.c:1000 [inline] >> posix_locks_deadlock fs/locks.c:1023 [inline] >> posix_lock_inode+0x1f9e/0x2750 fs/locks.c:1163 >> posix_lock_file fs/locks.c:1346 [inline] >> vfs_lock_file fs/locks.c:2314 [inline] >> vfs_lock_file+0xc7/0xf0 fs/locks.c:2309 >> do_lock_file_wait.part.0+0xe5/0x260 fs/locks.c:2328 >> do_lock_file_wait fs/locks.c:2324 [inline] >> fcntl_setlk+0x2f1/0xfe0 fs/locks.c:2413 >> do_fcntl+0x843/0x12b0 fs/fcntl.c:370 >> __do_sys_fcntl fs/fcntl.c:463 [inline] >> __se_sys_fcntl fs/fcntl.c:448 [inline] >> __x64_sys_fcntl+0x16d/0x1e0 fs/fcntl.c:448 >> do_syscall_64+0x1a3/0x800 arch/x86/entry/common.c:290 >> entry_SYSCALL_64_after_hwframe+0x49/0xbe >> RIP: 0033:0x457ec9 >> Code: 6d b7 fb ff c3 66 2e 0f 1f 84 00 00 00 00 00 66 90 48 89 f8 48 89 f7 >> 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff >> ff 0f 83 3b b7 fb ff c3 66 2e 0f 1f 84 00 00 00 00 >> RSP: 002b:00007f58bbb50c78 EFLAGS: 00000246 ORIG_RAX: 0000000000000048 >> RAX: ffffffffffffffda RBX: 0000000000000003 RCX: 0000000000457ec9 >> RDX: 0000000020000140 RSI: 0000000000000007 RDI: 0000000000000003 >> RBP: 000000000073bf00 R08: 0000000000000000 R09: 0000000000000000 >> R10: 0000000000000000 R11: 0000000000000246 R12: 00007f58bbb516d4 >> R13: 00000000004be5f0 R14: 00000000004ceab0 R15: 00000000ffffffff >> >> Allocated by task 10100: >> save_stack+0x45/0xd0 mm/kasan/common.c:73 >> set_track mm/kasan/common.c:85 [inline] >> kasan_kmalloc mm/kasan/common.c:482 [inline] >> kasan_kmalloc+0xcf/0xe0 mm/kasan/common.c:455 >> kasan_slab_alloc+0xf/0x20 mm/kasan/common.c:397 >> kmem_cache_alloc+0x12d/0x710 mm/slab.c:3541 >> kmem_cache_zalloc include/linux/slab.h:730 [inline] >> locks_alloc_lock+0x8e/0x2f0 fs/locks.c:344 >> fcntl_setlk+0xa9/0xfe0 fs/locks.c:2362 >> do_fcntl+0x843/0x12b0 fs/fcntl.c:370 >> __do_sys_fcntl fs/fcntl.c:463 [inline] >> __se_sys_fcntl fs/fcntl.c:448 [inline] >> __x64_sys_fcntl+0x16d/0x1e0 fs/fcntl.c:448 >> do_syscall_64+0x1a3/0x800 arch/x86/entry/common.c:290 >> entry_SYSCALL_64_after_hwframe+0x49/0xbe >> >> Freed by task 10100: >> save_stack+0x45/0xd0 mm/kasan/common.c:73 >> set_track mm/kasan/common.c:85 [inline] >> __kasan_slab_free+0x102/0x150 mm/kasan/common.c:444 >> kasan_slab_free+0xe/0x10 mm/kasan/common.c:452 >> __cache_free mm/slab.c:3485 [inline] >> kmem_cache_free+0x86/0x260 mm/slab.c:3747 >> locks_free_lock+0x27a/0x3f0 fs/locks.c:381 >> fcntl_setlk+0x7b5/0xfe0 fs/locks.c:2439 >> do_fcntl+0x843/0x12b0 fs/fcntl.c:370 >> __do_sys_fcntl fs/fcntl.c:463 [inline] >> __se_sys_fcntl fs/fcntl.c:448 [inline] >> __x64_sys_fcntl+0x16d/0x1e0 fs/fcntl.c:448 >> do_syscall_64+0x1a3/0x800 arch/x86/entry/common.c:290 >> entry_SYSCALL_64_after_hwframe+0x49/0xbe >> >> The buggy address belongs to the object at ffff88808791b000 >> which belongs to the cache file_lock_cache of size 264 >> The buggy address is located 0 bytes inside of >> 264-byte region [ffff88808791b000, ffff88808791b108) >> The buggy address belongs to the page: >> page:ffffea00021e46c0 count:1 mapcount:0 mapping:ffff8880aa16a1c0 index:0x0 >> flags: 0x1fffc0000000200(slab) >> raw: 01fffc0000000200 ffffea0002333508 ffffea00021d76c8 ffff8880aa16a1c0 >> raw: 0000000000000000 ffff88808791b000 000000010000000c 0000000000000000 >> page dumped because: kasan: bad access detected >> >> Memory state around the buggy address: >> ffff88808791af00: fb fb fb fb fb fb fb fc fc fc fc fc fc fc fc fc >> ffff88808791af80: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc >> > ffff88808791b000: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb >> ^ >> ffff88808791b080: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb >> ffff88808791b100: fb fc fc fc fc fc fc fc fc fb fb fb fb fb fb fb >> ================================================================== >> >> >> > > The interesting bit is that the crash, alloc and free all seem to have > occurred in the same kernel task (PID 10100). > > Here's the loop in what_owner_is_waiting_for(): > > ----------------8<------------------ > hash_for_each_possible(blocked_hash, fl, fl_link, posix_owner_key(block_fl)) { > if (posix_same_owner(fl, block_fl)) { > while (fl->fl_blocker) <<<<<< CRASH HERE > fl = fl->fl_blocker; > return fl; > } > } > ----------------8<------------------ > > So fl got freed while we were walking down the chain of blocked locks. > At a quick glance, I'm now wondering whether the lockless optimization > to avoid the blocked_lock_lock in locks_delete_block is actually ok. > > Neil, any thoughts? The repro didn't trigger for me, but code inspection suggested I should invest in brown paper bags. Note that while this patch clearly fixes a bug, and I suspect it is the cause of this report, I cannot confirm with testing as I cannot trigger the bug. I enabled KASAN and ran "qemu -smp 4" to no avail. Thanks, NeilBrown From: NeilBrown <neilb@xxxxxxxx> Date: Thu, 3 Jan 2019 10:59:50 +1100 Subject: [PATCH] locks: fix error in locks_move_blocks() After moving all requests from fl->fl_blocked_requests to new->fl_blocked_requests it is nonsensical to do anything to all the remaining elements, there aren't any. This should do something to all the requests that have been moved - for simplicity, it does it to all requests in the target list. Setting "f->fl_blocker = new" to all members of new->fl_blocked_requests is "obviously correct" as it preserves the invariant of the linkage among requests. Reported-by: syzbot+239d99847eb49ecb3899@xxxxxxxxxxxxxxxxxxxxxxxxx Fixes: 5946c4319ebb ("fs/locks: allow a lock request to block other requests.") Signed-off-by: NeilBrown <neilb@xxxxxxxx> --- fs/locks.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/fs/locks.c b/fs/locks.c index f0b24d98f36b..ff6af2c32601 100644 --- a/fs/locks.c +++ b/fs/locks.c @@ -453,7 +453,7 @@ static void locks_move_blocks(struct file_lock *new, struct file_lock *fl) return; spin_lock(&blocked_lock_lock); list_splice_init(&fl->fl_blocked_requests, &new->fl_blocked_requests); - list_for_each_entry(f, &fl->fl_blocked_requests, fl_blocked_member) + list_for_each_entry(f, &new->fl_blocked_requests, fl_blocked_member) f->fl_blocker = new; spin_unlock(&blocked_lock_lock); } -- 2.14.0.rc0.dirty
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