On Tue, Oct 25, 2022 at 1:49 AM Matthew Wilcox wrote: > > Adding the nilfs maintainers ... > > On Mon, Oct 24, 2022 at 09:38:40AM -0700, syzbot wrote: > > Hello, > > > > syzbot found the following issue on: > > > > HEAD commit: bbed346d5a96 Merge branch 'for-next/core' into for-kernelci > > git tree: git://git.kernel.org/pub/scm/linux/kernel/git/arm64/linux.git for-kernelci > > console output: https://syzkaller.appspot.com/x/log.txt?x=15788ec2880000 > > kernel config: https://syzkaller.appspot.com/x/.config?x=3a4a45d2d827c1e > > dashboard link: https://syzkaller.appspot.com/bug?extid=f1eb7f33bbf683a5e1e1 > > compiler: Debian clang version 13.0.1-++20220126092033+75e33f71c2da-1~exp1~20220126212112.63, GNU ld (GNU Binutils for Debian) 2.35.2 > > userspace arch: arm64 > > > > Unfortunately, I don't have any reproducer for this issue yet. > > > > Downloadable assets: > > disk image: https://storage.googleapis.com/syzbot-assets/e8e91bc79312/disk-bbed346d.raw.xz > > vmlinux: https://storage.googleapis.com/syzbot-assets/c1cb3fb3b77e/vmlinux-bbed346d.xz > > > > IMPORTANT: if you fix the issue, please add the following tag to the commit: > > Reported-by: syzbot+f1eb7f33bbf683a5e1e1@xxxxxxxxxxxxxxxxxxxxxxxxx > > > > Unable to handle kernel NULL pointer dereference at virtual address 0000000000000050 > > Mem abort info: > > ESR = 0x0000000096000005 > > EC = 0x25: DABT (current EL), IL = 32 bits > > SET = 0, FnV = 0 > > EA = 0, S1PTW = 0 > > FSC = 0x05: level 1 translation fault > > Data abort info: > > ISV = 0, ISS = 0x00000005 > > CM = 0, WnR = 0 > > user pgtable: 4k pages, 48-bit VAs, pgdp=000000014a8d0000 > > [0000000000000050] pgd=08000001532c9003, p4d=08000001532c9003, pud=0000000000000000 > > Internal error: Oops: 0000000096000005 [#1] PREEMPT SMP > > Modules linked in: > > CPU: 0 PID: 3066 Comm: syz-executor.3 Not tainted 6.0.0-rc7-syzkaller-18095-gbbed346d5a96 #0 > > Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 09/30/2022 > > pstate: 80400005 (Nzcv daif +PAN -UAO -TCO -DIT -SSBS BTYPE=--) > > pc : filemap_free_folio+0x20/0x288 mm/filemap.c:231 > > lr : filemap_free_folio+0x1c/0x288 mm/filemap.c:227 > > sp : ffff80001280b990 > > x29: ffff80001280b990 x28: ffff000117b4ea00 x27: 0000000000000000 > > x26: 0000000000000001 x25: ffff80000cb6fd9e x24: fffffffffffffffe > > x23: 0000000000000000 x22: fffffc0004cfa8c0 x21: 0000000000000001 > > x20: ffff0001127af450 x19: fffffc0004cfa8c0 x18: 00000000000003b8 > > x17: ffff80000bffd6bc x16: 0000000000000002 x15: 0000000000000000 > > x14: 0000000000000000 x13: 0000000000000003 x12: ffff80000d5f02b0 > > x11: ff808000083c31e8 x10: 0000000000000000 x9 : ffff8000083c31e8 > > x8 : 0000000000000000 x7 : ffff80000856806c x6 : 0000000000000000 > > x5 : 0000000000000080 x4 : 0000000000000000 x3 : 0000000000000000 > > x2 : 0000000000000006 x1 : fffffc0004cfa8c0 x0 : ffff0001127af450 > > Call trace: > > filemap_free_folio+0x20/0x288 mm/filemap.c:231 > > delete_from_page_cache_batch+0x148/0x184 mm/filemap.c:341 > > truncate_inode_pages_range+0x174/0xb94 mm/truncate.c:370 > > truncate_inode_pages mm/truncate.c:452 [inline] > > truncate_inode_pages_final+0x8c/0x9c mm/truncate.c:487 > > nilfs_evict_inode+0x58/0x1cc fs/nilfs2/inode.c:906 > > evict+0xec/0x334 fs/inode.c:665 > > dispose_list fs/inode.c:698 [inline] > > evict_inodes+0x2e0/0x354 fs/inode.c:748 > > generic_shutdown_super+0x50/0x190 fs/super.c:480 > > kill_block_super+0x30/0x78 fs/super.c:1427 > > deactivate_locked_super+0x70/0xe8 fs/super.c:332 > > deactivate_super+0xd0/0xd4 fs/super.c:363 > > cleanup_mnt+0x1f8/0x234 fs/namespace.c:1186 > > __cleanup_mnt+0x20/0x30 fs/namespace.c:1193 > > task_work_run+0xc4/0x14c kernel/task_work.c:177 > > resume_user_mode_work include/linux/resume_user_mode.h:49 [inline] > > do_notify_resume+0x174/0x1f0 arch/arm64/kernel/signal.c:1127 > > prepare_exit_to_user_mode arch/arm64/kernel/entry-common.c:137 [inline] > > exit_to_user_mode arch/arm64/kernel/entry-common.c:142 [inline] > > el0_svc+0x9c/0x150 arch/arm64/kernel/entry-common.c:637 > > el0t_64_sync_handler+0x84/0xf0 arch/arm64/kernel/entry-common.c:654 > > el0t_64_sync+0x18c/0x190 arch/arm64/kernel/entry.S:581 > > Code: aa0103f3 aa0003f4 97fb728c f940de88 (f9402914) > > ---[ end trace 0000000000000000 ]--- > > ---------------- > > Code disassembly (best guess): > > 0: aa0103f3 mov x19, x1 > > 4: aa0003f4 mov x20, x0 > > 8: 97fb728c bl 0xffffffffffedca38 > > c: f940de88 ldr x8, [x20, #440] > > * 10: f9402914 ldr x20, [x8, #80] <-- trapping instruction > > As far as I can tell, this is: > > free_folio = mapping->a_ops->free_folio; > > and the first dereference (mapping->a_ops) is offset 440 from mapping, > which works fine, but is NULL. So loading aops->free_folio is the > NULL pointer dereference. > > So does nilfs have an address_space with a NULL a_ops? That doesn't > seem to be allowed; at least I don't see any checks of a_ops for > being NULL in the rest of the VFS or MM. There is no place where a NULL is set to a_ops in NILFS. All inodes used by NILFS are allocated by either iget5_locked() or new_inode(), and both of them at least initialize a_ops to &empty_aops with inode_init_always(). So, I suspect this is caused by UAF or, less likely, a memory corruption on inode->i_data. I'm tracking these possibilities, but haven't been able to identify the cause. One possibility is that this is a variant of the report bug [1], which can cause an inode UAF: [1] https://syzkaller.appspot.com/bug?extid=b8c672b0e22615c80fe0 If so, this is fixed in 6.1-rc1, but not enough evidence yet if it's the same bug. Regards, Ryusuke Konishi
