On Sat, 4 Sept 2021 at 20:58, syzbot <syzbot+d08efd12a2905a344291@xxxxxxxxxxxxxxxxxxxxxxxxx> wrote: > > Hello, > > syzbot found the following issue on: > > HEAD commit: 835d31d319d9 Merge tag 'media/v5.15-1' of git://git.kernel.. > git tree: upstream > console output: https://syzkaller.appspot.com/x/log.txt?x=1189fe49300000 > kernel config: https://syzkaller.appspot.com/x/.config?x=d1a7a34dc082816f > dashboard link: https://syzkaller.appspot.com/bug?extid=d08efd12a2905a344291 > compiler: gcc (Debian 10.2.1-6) 10.2.1 20210110, GNU ld (GNU Binutils for Debian) 2.35.1 > > IMPORTANT: if you fix the issue, please add the following tag to the commit: > Reported-by: syzbot+d08efd12a2905a344291@xxxxxxxxxxxxxxxxxxxxxxxxx > > ================================================================== > BUG: KFENCE: use-after-free read in kvm_fastop_exception+0xf6d/0x105b > > Use-after-free read at 0xffff88823bc0c020 (in kfence-#5): > kvm_fastop_exception+0xf6d/0x105b There is probably some bug in d_lookup, but there is also something wrong with the unwinder. It prints an unrelated kvm_fastop_exception frame instead of __d_lookup and interestingly a very similar thing happens on arm64 with HWASAN and a similar bug in d_lookup. The corresponding report is: https://syzkaller.appspot.com/bug?extid=488ddf8087564d6de6e2 BUG: KASAN: invalid-access in __entry_tramp_text_end+0xddc/0xd000 CPU: 0 PID: 22 Comm: kdevtmpfs Not tainted 5.14.0-syzkaller-11152-g78e709522d2c #0 Hardware name: linux,dummy-virt (DT) Call trace: dump_backtrace+0x0/0x1ac arch/arm64/kernel/stacktrace.c:76 show_stack+0x18/0x24 arch/arm64/kernel/stacktrace.c:215 __dump_stack lib/dump_stack.c:88 [inline] dump_stack_lvl+0x68/0x84 lib/dump_stack.c:106 print_address_description+0x7c/0x2b4 mm/kasan/report.c:256 __kasan_report mm/kasan/report.c:442 [inline] kasan_report+0x134/0x380 mm/kasan/report.c:459 __do_kernel_fault+0x128/0x1bc arch/arm64/mm/fault.c:317 do_bad_area arch/arm64/mm/fault.c:466 [inline] do_tag_check_fault+0x74/0x90 arch/arm64/mm/fault.c:737 do_mem_abort+0x44/0xb4 arch/arm64/mm/fault.c:813 el1_abort+0x40/0x60 arch/arm64/kernel/entry-common.c:357 el1h_64_sync_handler+0xb0/0xd0 arch/arm64/kernel/entry-common.c:408 el1h_64_sync+0x78/0x7c arch/arm64/kernel/entry.S:567 __entry_tramp_text_end+0xddc/0xd000 d_lookup+0x44/0x70 fs/dcache.c:2370 lookup_dcache+0x24/0x84 fs/namei.c:1520 __lookup_hash+0x24/0xd0 fs/namei.c:1543 kern_path_locked+0x90/0x10c fs/namei.c:2567 handle_remove+0x38/0x284 drivers/base/devtmpfs.c:312 handle drivers/base/devtmpfs.c:382 [inline] devtmpfs_work_loop drivers/base/devtmpfs.c:395 [inline] devtmpfsd+0x8c/0xd0 drivers/base/devtmpfs.c:437 kthread+0x150/0x15c kernel/kthread.c:319 ret_from_fork+0x10/0x20 arch/arm64/kernel/entry.S:756 Here kernel unwinder prints __entry_tramp_text_end instead of __d_lookup. I've looked in more detail into the arm64 case: d_lookup contains a static call to __d_lookup as expected: ffff8000102e0780 <d_lookup>: ... ffff8000102e07c0: 97ffffa4 bl ffff8000102e0650 <__d_lookup> ... ffff8000102e07e8: d65f03c0 ret and these symbols don't overlap or something: $ aarch64-linux-gnu-nm -nS vmlinux | egrep -C 1 " (t|T) (__entry_tramp_text|__d_lookup)" ffff8000102e01f0 0000000000000458 T d_alloc_parallel ffff8000102e0650 0000000000000128 T __d_lookup ffff8000102e0780 000000000000006c T d_lookup -- ffff8000117a1f88 T __hibernate_exit_text_end ffff8000117a2000 T __entry_tramp_text_start ffff8000117a2000 00000000000007c8 T tramp_vectors -- ffff8000117a27f0 0000000000000024 T tramp_exit_compat ffff8000117a3000 T __entry_tramp_text_end ffff8000117b0000 D _etext So it looks like in both cases the top fault frame is just wrong. But I would assume it's extracted by arch-dependent code, so it's suspicious that it affects both x86 and arm64... Any ideas what's happening? > d_lookup+0xd8/0x170 fs/dcache.c:2370 > lookup_dcache+0x1e/0x130 fs/namei.c:1520 > __lookup_hash+0x29/0x180 fs/namei.c:1543 > kern_path_locked+0x17e/0x320 fs/namei.c:2567 > handle_remove+0xa2/0x5fe drivers/base/devtmpfs.c:312 > handle drivers/base/devtmpfs.c:382 [inline] > devtmpfs_work_loop drivers/base/devtmpfs.c:395 [inline] > devtmpfsd+0x1b9/0x2a3 drivers/base/devtmpfs.c:437 > kthread+0x3e5/0x4d0 kernel/kthread.c:319 > ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:295 > > kfence-#5 [0xffff88823bc0c000-0xffff88823bc0cfff, size=4096, cache=names_cache] allocated by task 22: > getname_kernel+0x4e/0x370 fs/namei.c:226 > kern_path_locked+0x71/0x320 fs/namei.c:2558 > handle_remove+0xa2/0x5fe drivers/base/devtmpfs.c:312 > handle drivers/base/devtmpfs.c:382 [inline] > devtmpfs_work_loop drivers/base/devtmpfs.c:395 [inline] > devtmpfsd+0x1b9/0x2a3 drivers/base/devtmpfs.c:437 > kthread+0x3e5/0x4d0 kernel/kthread.c:319 > ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:295 > > freed by task 22: > putname.part.0+0xe1/0x120 fs/namei.c:270 > putname include/linux/err.h:41 [inline] > filename_parentat fs/namei.c:2547 [inline] > kern_path_locked+0xc2/0x320 fs/namei.c:2558 > handle_remove+0xa2/0x5fe drivers/base/devtmpfs.c:312 > handle drivers/base/devtmpfs.c:382 [inline] > devtmpfs_work_loop drivers/base/devtmpfs.c:395 [inline] > devtmpfsd+0x1b9/0x2a3 drivers/base/devtmpfs.c:437 > kthread+0x3e5/0x4d0 kernel/kthread.c:319 > ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:295 > > CPU: 1 PID: 22 Comm: kdevtmpfs Not tainted 5.14.0-syzkaller #0 > Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011 > RIP: 0010:kvm_fastop_exception+0xf6d/0x105b > Code: d3 ed e9 14 1b 6d f8 49 8d 0e 48 83 e1 f8 4c 8b 21 41 8d 0e 83 e1 07 c1 e1 03 49 d3 ec e9 6a 28 6d f8 49 8d 4d 00 48 83 e1 f8 <4c> 8b 21 41 8d 4d 00 83 e1 07 c1 e1 03 49 d3 ec e9 5a 32 6d f8 bd > RSP: 0018:ffffc90000fe7ae8 EFLAGS: 00010282 > RAX: 0000000035736376 RBX: ffff88803b141cc0 RCX: ffff88823bc0c020 > RDX: ffffed100762839f RSI: 0000000000000004 RDI: 0000000000000007 > RBP: 0000000000000004 R08: 0000000000000000 R09: ffff88803b141cf0 > R10: ffffed100762839e R11: 0000000000000000 R12: ffff88823bc0c020 > R13: ffff88823bc0c020 R14: ffff88803b141cf0 R15: dffffc0000000000 > FS: 0000000000000000(0000) GS:ffff8880b9d00000(0000) knlGS:0000000000000000 > CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 > CR2: ffff88823bc0c020 CR3: 0000000029892000 CR4: 00000000001506e0 > DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 > DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400 > Call Trace: > d_lookup+0xd8/0x170 fs/dcache.c:2370 > lookup_dcache+0x1e/0x130 fs/namei.c:1520 > __lookup_hash+0x29/0x180 fs/namei.c:1543 > kern_path_locked+0x17e/0x320 fs/namei.c:2567 > handle_remove+0xa2/0x5fe drivers/base/devtmpfs.c:312 > handle drivers/base/devtmpfs.c:382 [inline] > devtmpfs_work_loop drivers/base/devtmpfs.c:395 [inline] > devtmpfsd+0x1b9/0x2a3 drivers/base/devtmpfs.c:437 > kthread+0x3e5/0x4d0 kernel/kthread.c:319 > ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:295 > ================================================================== > ---------------- > Code disassembly (best guess): > 0: d3 ed shr %cl,%ebp > 2: e9 14 1b 6d f8 jmpq 0xf86d1b1b > 7: 49 8d 0e lea (%r14),%rcx > a: 48 83 e1 f8 and $0xfffffffffffffff8,%rcx > e: 4c 8b 21 mov (%rcx),%r12 > 11: 41 8d 0e lea (%r14),%ecx > 14: 83 e1 07 and $0x7,%ecx > 17: c1 e1 03 shl $0x3,%ecx > 1a: 49 d3 ec shr %cl,%r12 > 1d: e9 6a 28 6d f8 jmpq 0xf86d288c > 22: 49 8d 4d 00 lea 0x0(%r13),%rcx > 26: 48 83 e1 f8 and $0xfffffffffffffff8,%rcx > * 2a: 4c 8b 21 mov (%rcx),%r12 <-- trapping instruction > 2d: 41 8d 4d 00 lea 0x0(%r13),%ecx > 31: 83 e1 07 and $0x7,%ecx > 34: c1 e1 03 shl $0x3,%ecx > 37: 49 d3 ec shr %cl,%r12 > 3a: e9 5a 32 6d f8 jmpq 0xf86d3299 > 3f: bd .byte 0xbd > > > --- > This report 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 issue. See: > https://goo.gl/tpsmEJ#status for how to communicate with syzbot.
