Re: [syzbot] [bcachefs?] UBSAN: array-index-out-of-bounds in bch2_btree_path_traverse_cached_slowpath

From: Kent Overstreet
Date: Tue May 28 2024 - 21:46:37 EST

On Tue, May 28, 2024 at 01:13:23AM -0700, syzbot wrote:
> Hello,
>
> syzbot found the following issue on:
>
> HEAD commit: 2bfcfd584ff5 Merge tag 'pmdomain-v6.10-rc1' of git://git.k..
> git tree: upstream
> console output: https://syzkaller.appspot.com/x/log.txt?x=1674fd44980000
> kernel config: https://syzkaller.appspot.com/x/.config?x=733cc7a95171d8e7
> dashboard link: https://syzkaller.appspot.com/bug?extid=fa3fc4c486ec9c342fcc
> compiler: gcc (Debian 12.2.0-14) 12.2.0, GNU ld (GNU Binutils for Debian) 2.40
> userspace arch: i386
>
> Unfortunately, I don't have any reproducer for this issue yet.
>
> Downloadable assets:
> disk image (non-bootable): https://storage.googleapis.com/syzbot-assets/7bc7510fe41f/non_bootable_disk-2bfcfd58.raw.xz
> vmlinux: https://storage.googleapis.com/syzbot-assets/c7ed3bb80bed/vmlinux-2bfcfd58.xz
> kernel image: https://storage.googleapis.com/syzbot-assets/93acc5bfbaef/bzImage-2bfcfd58.xz
>
> IMPORTANT: if you fix the issue, please add the following tag to the commit:
> Reported-by: syzbot+fa3fc4c486ec9c342fcc@xxxxxxxxxxxxxxxxxxxxxxxxx
>
> bcachefs (loop2): journal_replay... done
> bcachefs (loop2): resume_logged_ops... done
> bcachefs (loop2): going read-write
> bcachefs (loop2): done starting filesystem
> ------------[ cut here ]------------
> UBSAN: array-index-out-of-bounds in fs/bcachefs/btree_key_cache.c:215:16
> index 66 is out of range for type 'bkey_cached *[16]'

So, this is an odd one - the number of elements on the percpu freelist
was somehow set to 64.

And it wasn't a buffer overrun, 64 isn't a pointer.

Perhaps there's a bug in the percpu allocator and it's not zeroing
correctly? That would fit, since we're seeing it on startup.

> CPU: 1 PID: 7694 Comm: syz-executor.2 Not tainted 6.10.0-rc1-syzkaller-00013-g2bfcfd584ff5 #0
> Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.2-debian-1.16.2-1 04/01/2014
> Call Trace:
> <TASK>
> __dump_stack lib/dump_stack.c:88 [inline]
> dump_stack_lvl+0x16c/0x1f0 lib/dump_stack.c:114
> ubsan_epilogue lib/ubsan.c:231 [inline]
> __ubsan_handle_out_of_bounds+0x110/0x150 lib/ubsan.c:429
> bkey_cached_alloc fs/bcachefs/btree_key_cache.c:215 [inline]
> btree_key_cache_create fs/bcachefs/btree_key_cache.c:329 [inline]
> bch2_btree_path_traverse_cached_slowpath+0x4304/0x4d90 fs/bcachefs/btree_key_cache.c:484
> bch2_btree_path_traverse_cached+0x9ec/0xdc0 fs/bcachefs/btree_key_cache.c:587
> bch2_btree_path_traverse_one+0x16b4/0x2e40 fs/bcachefs/btree_iter.c:1158
> bch2_btree_path_traverse fs/bcachefs/btree_iter.h:229 [inline]
> bch2_btree_path_traverse fs/bcachefs/btree_iter.h:221 [inline]
> bch2_btree_iter_peek_slot+0x715/0x2450 fs/bcachefs/btree_iter.c:2603
> __bch2_bkey_get_iter fs/bcachefs/btree_iter.h:552 [inline]
> bch2_bkey_get_iter fs/bcachefs/btree_iter.h:566 [inline]
> bch2_inode_peek_nowarn+0x1e3/0x390 fs/bcachefs/inode.c:340
> bch2_inode_peek fs/bcachefs/inode.c:366 [inline]
> bch2_inode_find_by_inum_trans+0x125/0x2a0 fs/bcachefs/inode.c:939
> bch2_vfs_inode_get+0x41f/0x550 fs/bcachefs/fs.c:277
> bch2_mount+0xc81/0x1090 fs/bcachefs/fs.c:1999
> legacy_get_tree+0x109/0x220 fs/fs_context.c:662
> vfs_get_tree+0x8f/0x380 fs/super.c:1780
> do_new_mount fs/namespace.c:3352 [inline]
> path_mount+0x6e1/0x1f10 fs/namespace.c:3679
> do_mount fs/namespace.c:3692 [inline]
> __do_sys_mount fs/namespace.c:3898 [inline]
> __se_sys_mount fs/namespace.c:3875 [inline]
> __ia32_sys_mount+0x295/0x320 fs/namespace.c:3875
> do_syscall_32_irqs_on arch/x86/entry/common.c:165 [inline]
> __do_fast_syscall_32+0x73/0x120 arch/x86/entry/common.c:386
> do_fast_syscall_32+0x32/0x80 arch/x86/entry/common.c:411
> entry_SYSENTER_compat_after_hwframe+0x84/0x8e
> RIP: 0023:0xf72f3579
> Code: b8 01 10 06 03 74 b4 01 10 07 03 74 b0 01 10 08 03 74 d8 01 00 00 00 00 00 00 00 00 00 00 00 00 00 51 52 55 89 e5 0f 34 cd 80 <5d> 5a 59 c3 90 90 90 90 8d b4 26 00 00 00 00 8d b4 26 00 00 00 00
> RSP: 002b:00000000f5ee5400 EFLAGS: 00000292 ORIG_RAX: 0000000000000015
> RAX: ffffffffffffffda RBX: 00000000f5ee5460 RCX: 0000000020011a40
> RDX: 0000000020000040 RSI: 0000000001200014 RDI: 00000000f5ee54a0
> RBP: 00000000f5ee5460 R08: 0000000000000000 R09: 0000000000000000
> R10: 0000000000000000 R11: 0000000000000296 R12: 0000000000000000
> R13: 0000000000000000 R14: 0000000000000000 R15: 0000000000000000
> </TASK>
> ---[ end trace ]---
> ----------------
> Code disassembly (best guess), 2 bytes skipped:
> 0: 10 06 adc %al,(%rsi)
> 2: 03 74 b4 01 add 0x1(%rsp,%rsi,4),%esi
> 6: 10 07 adc %al,(%rdi)
> 8: 03 74 b0 01 add 0x1(%rax,%rsi,4),%esi
> c: 10 08 adc %cl,(%rax)
> e: 03 74 d8 01 add 0x1(%rax,%rbx,8),%esi
> 1e: 00 51 52 add %dl,0x52(%rcx)
> 21: 55 push %rbp
> 22: 89 e5 mov %esp,%ebp
> 24: 0f 34 sysenter
> 26: cd 80 int $0x80
> * 28: 5d pop %rbp <-- trapping instruction
> 29: 5a pop %rdx
> 2a: 59 pop %rcx
> 2b: c3 ret
> 2c: 90 nop
> 2d: 90 nop
> 2e: 90 nop
> 2f: 90 nop
> 30: 8d b4 26 00 00 00 00 lea 0x0(%rsi,%riz,1),%esi
> 37: 8d b4 26 00 00 00 00 lea 0x0(%rsi,%riz,1),%esi
>
>
> ---
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>
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