Hi, On 13.09.2018 11:00, syzbot wrote: > Hello, > > syzbot found the following crash on: > > HEAD commit: 54eda9df17f3 Merge tag 'pci-v4.19-fixes-1' of git://git.ke.. > git tree: upstream > console output: https://syzkaller.appspot.com/x/log.txt?x=109a3d9e400000 what are requests id written here: write$FUSE_INIT(r0, &(0x7f0000000100)={0x50, 0x0, 0x1}, 0x50) write$FUSE_STATFS(r0, &(0x7f0000000040)={0x60, 0x0, 0x2, {{0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0xfffffffffffffffa}}}, 0x60) ? In case of parallel thread called write with id, we just queued to processing in fuse_dev_do_read(), we may bump to this stack (despite read has not finished yet, syzbot may write just everything, any id). fuse_dev_do_read() fuse_dev_do_write() list_move_tail(&req->list, &fpq->processing); ... spin_unlock(&fpq->lock); ... ... request_end(fc, req); ... fuse_put_request(fc, req); if (test_bit(FR_INTERRUPTED, &req->flags)) queue_interrupt(fiq, req); We should keep req refcount in fuse_dev_do_read(), till we haven't finished to use it. Something like this (compile tested only): diff --git a/fs/fuse/dev.c b/fs/fuse/dev.c index 11ea2c4a38ab..675caed3e655 100644 --- a/fs/fuse/dev.c +++ b/fs/fuse/dev.c @@ -1311,12 +1311,14 @@ static ssize_t fuse_dev_do_read(struct fuse_dev *fud, struct file *file, goto out_end; } list_move_tail(&req->list, &fpq->processing); + __fuse_get_request(req); spin_unlock(&fpq->lock); set_bit(FR_SENT, &req->flags); /* matches barrier in request_wait_answer() */ smp_mb__after_atomic(); if (test_bit(FR_INTERRUPTED, &req->flags)) queue_interrupt(fiq, req); + fuse_put_request(fc, req); return reqsize; > kernel config: https://syzkaller.appspot.com/x/.config?x=b8f349d23d3c4835 > dashboard link: https://syzkaller.appspot.com/bug?extid=4e975615ca01f2277bdd > compiler: gcc (GCC) 8.0.1 20180413 (experimental) > > Unfortunately, I don't have any reproducer for this crash yet. > > IMPORTANT: if you fix the bug, please add the following tag to the commit: > Reported-by: syzbot+4e975615ca01f2277bdd@xxxxxxxxxxxxxxxxxxxxxxxxx > > ================================================================== > BUG: KASAN: use-after-free in constant_test_bit arch/x86/include/asm/bitops.h:328 [inline] > BUG: KASAN: use-after-free in fuse_dev_do_read.isra.27+0x1659/0x1920 fs/fuse/dev.c:1318 > Read of size 8 at addr ffff8801cbd4ea30 by task syz-executor0/28821 > > CPU: 1 PID: 28821 Comm: syz-executor0 Not tainted 4.19.0-rc3+ #11 > 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+0x1c4/0x2b4 lib/dump_stack.c:113 > print_address_description.cold.8+0x9/0x1ff mm/kasan/report.c:256 > kasan_report_error mm/kasan/report.c:354 [inline] > kasan_report.cold.9+0x242/0x309 mm/kasan/report.c:412 > __asan_report_load8_noabort+0x14/0x20 mm/kasan/report.c:433 > constant_test_bit arch/x86/include/asm/bitops.h:328 [inline] > fuse_dev_do_read.isra.27+0x1659/0x1920 fs/fuse/dev.c:1318 > fuse_dev_read+0x1a9/0x250 fs/fuse/dev.c:1360 > call_read_iter include/linux/fs.h:1801 [inline] > new_sync_read fs/read_write.c:406 [inline] > __vfs_read+0x6ac/0x9b0 fs/read_write.c:418 > vfs_read+0x17f/0x3c0 fs/read_write.c:452 > ksys_read+0x101/0x260 fs/read_write.c:578 > __do_sys_read fs/read_write.c:588 [inline] > __se_sys_read fs/read_write.c:586 [inline] > __x64_sys_read+0x73/0xb0 fs/read_write.c:586 > do_syscall_64+0x1b9/0x820 arch/x86/entry/common.c:290 > entry_SYSCALL_64_after_hwframe+0x49/0xbe > RIP: 0033:0x4572d9 > Code: fd b4 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 cb b4 fb ff c3 66 2e 0f 1f 84 00 00 00 00 > RSP: 002b:00007faaeefe4c78 EFLAGS: 00000246 ORIG_RAX: 0000000000000000 > RAX: ffffffffffffffda RBX: 00007faaeefe56d4 RCX: 00000000004572d9 > RDX: 0000000000001000 RSI: 00000000200040c0 RDI: 0000000000000003 > RBP: 00000000009300a0 R08: 0000000000000000 R09: 0000000000000000 > R10: 0000000000000000 R11: 0000000000000246 R12: 00000000ffffffff > R13: 00000000004d4508 R14: 00000000004c8d44 R15: 0000000000000000 > > Allocated by task 28825: > save_stack+0x43/0xd0 mm/kasan/kasan.c:448 > set_track mm/kasan/kasan.c:460 [inline] > kasan_kmalloc+0xc7/0xe0 mm/kasan/kasan.c:553 > kasan_slab_alloc+0x12/0x20 mm/kasan/kasan.c:490 > kmem_cache_alloc+0x12e/0x730 mm/slab.c:3554 > __fuse_request_alloc+0x27/0xf0 fs/fuse/dev.c:58 > fuse_request_alloc fs/fuse/dev.c:89 [inline] > __fuse_get_req+0x1f7/0x9e0 fs/fuse/dev.c:164 > fuse_get_req fs/fuse/dev.c:194 [inline] > fuse_simple_request+0x28/0x730 fs/fuse/dev.c:549 > fuse_statfs+0x368/0x8a0 fs/fuse/inode.c:442 > statfs_by_dentry+0x136/0x210 fs/statfs.c:64 > vfs_statfs+0x47/0x2e0 fs/statfs.c:74 > user_statfs+0xbd/0x150 fs/statfs.c:89 > __do_sys_statfs+0x7f/0xf0 fs/statfs.c:179 > __se_sys_statfs fs/statfs.c:176 [inline] > __x64_sys_statfs+0x54/0x80 fs/statfs.c:176 > do_syscall_64+0x1b9/0x820 arch/x86/entry/common.c:290 > entry_SYSCALL_64_after_hwframe+0x49/0xbe > > Freed by task 28825: > save_stack+0x43/0xd0 mm/kasan/kasan.c:448 > set_track mm/kasan/kasan.c:460 [inline] > __kasan_slab_free+0x102/0x150 mm/kasan/kasan.c:521 > kasan_slab_free+0xe/0x10 mm/kasan/kasan.c:528 > __cache_free mm/slab.c:3498 [inline] > kmem_cache_free+0x83/0x290 mm/slab.c:3756 > fuse_request_free+0x8b/0xa0 fs/fuse/dev.c:104 > fuse_put_request+0x2a6/0x350 fs/fuse/dev.c:304 > fuse_simple_request+0x453/0x730 fs/fuse/dev.c:571 > fuse_statfs+0x368/0x8a0 fs/fuse/inode.c:442 > statfs_by_dentry+0x136/0x210 fs/statfs.c:64 > vfs_statfs+0x47/0x2e0 fs/statfs.c:74 > user_statfs+0xbd/0x150 fs/statfs.c:89 > __do_sys_statfs+0x7f/0xf0 fs/statfs.c:179 > __se_sys_statfs fs/statfs.c:176 [inline] > __x64_sys_statfs+0x54/0x80 fs/statfs.c:176 > do_syscall_64+0x1b9/0x820 arch/x86/entry/common.c:290 > entry_SYSCALL_64_after_hwframe+0x49/0xbe > > The buggy address belongs to the object at ffff8801cbd4ea00 > which belongs to the cache fuse_request of size 448 > The buggy address is located 48 bytes inside of > 448-byte region [ffff8801cbd4ea00, ffff8801cbd4ebc0) > The buggy address belongs to the page: > page:ffffea00072f5380 count:1 mapcount:0 mapping:ffff8801d4ad4840 index:0x0 > flags: 0x2fffc0000000100(slab) > raw: 02fffc0000000100 ffffea000717eb48 ffff8801d4ad5c48 ffff8801d4ad4840 > raw: 0000000000000000 ffff8801cbd4e000 0000000100000008 0000000000000000 > page dumped because: kasan: bad access detected > > Memory state around the buggy address: > ffff8801cbd4e900: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc > ffff8801cbd4e980: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc >> ffff8801cbd4ea00: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb > ^ > ffff8801cbd4ea80: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb > ffff8801cbd4eb00: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb > ================================================================== > > > --- > 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#bug-status-tracking for how to communicate with syzbot.
