Message-ID: <686272db.a70a0220.3b7e22.0db2.GAE@google.com>
Date: Mon, 30 Jun 2025 04:19:55 -0700
From: syzbot <syzbot+5e43fb34e0478e83681c@...kaller.appspotmail.com>
To: kapoorarnav43@...il.com
Cc: kapoorarnav43@...il.com, linux-kernel@...r.kernel.org, 
	syzkaller-bugs@...glegroups.com
Subject: Re: Private message regarding: [syzbot] [bcachefs?] kernel BUG in bch2_journal_keys_peek_prev_min

> #syz test 
>
> 0001-bcachefs-avoid-BUG-when-journal-index-is-out-of-bounds.patch
>
> From 56f5b5e4abcde123456789012345678901234567 Mon Sep 17 00:00:00 2001
> From: Arnav Kapoor <kapoor...@...il.com <https://groups.google.com/u/1/>>
> Date: Sat, 29 Jun 2025 17:05:00 +0000
> Subject: [PATCH] bcachefs: avoid BUG when journal index is out of bounds
>
> Replace BUG_ON(*idx > keys->nr) with a proper bounds check.  
> Log an error and safely return NULL if idx is invalid, instead of crashing.
>
> Fixes a kernel BUG triggered by syzbot when calling
> bch2_journal_keys_peek_prev_min with invalid idx.
>
> Reported-by: syzbot+5e43fb...@...kaller.appspotmail.com 
> <https://groups.google.com/u/1/>
> Signed-off-by: Arnav Kapoor <kapoor...@...il.com 
> <https://groups.google.com/u/1/>>
> ---
>  fs/bcachefs/btree_journal_iter.c | 10 +++++++++-
>  1 file changed, 9 insertions(+), 1 deletion(-)
>
> diff --git a/fs/bcachefs/btree_journal_iter.c 
> b/fs/bcachefs/btree_journal_iter.c
> index 0123456789ab..abcdef012345 100644
> --- a/fs/bcachefs/btree_journal_iter.c
> +++ b/fs/bcachefs/btree_journal_iter.c
> @@
>  struct bkey_i *bch2_journal_keys_peek_prev_min(struct bch_fs *c, enum 
> btree_id btree_id,
>         unsigned level, struct bpos pos,
>         struct bpos end_pos, size_t *idx)
>  {
>   struct journal_keys *keys = &c->journal_keys;
>   unsigned iters = 0;
>   struct journal_key *k;
>  
> - BUG_ON(*idx > keys->nr);
> + if (unlikely(*idx > keys->nr)) {
> + pr_err("bch2_journal_keys_peek_prev_min: invalid idx %zu > nr %zu\n",
> +        *idx, keys->nr);
> + return NULL;
> + }
> +
> + if (!keys->nr)
> + return NULL;
>  
>  search:
>   if (!*idx)
>   *idx = __bch2_journal_key_search(keys, btree_id, level, pos);
>  
>   while (*idx &&
>          __journal_key_cmp(btree_id, level, end_pos, idx_to_key(keys, *idx 
> - 1)) <= 0) {
>   (*idx)++;
>   iters++;
>   if (iters == 10) {
>   *idx = 0;
>   goto search;
>   }
>   }
>  
>   return (*idx && *idx <= keys->nr) ? idx_to_key(keys, *idx - 1) : NULL;
>  }
> -- 
> 2.40.1
>
>
> On Sunday, 29 June 2025 at 22:25:29 UTC+5:30 syzbot wrote:
>
> Hello, 
>
> syzbot found the following issue on: 
>
> HEAD commit: 7595b66ae9de Merge tag 'selinux-pr-20250624' of git://git... 
> git tree: upstream 
> console output: https://syzkaller.appspot.com/x/log.txt?x=10edd182580000 
> kernel config: https://syzkaller.appspot.com/x/.config?x=79da270cec5ffd65 
> dashboard link: https://syzkaller.appspot.com/bug?extid=5e43fb34e0478e83681c 
> compiler: Debian clang version 20.1.6 
> (++20250514063057+1e4d39e07757-1~exp1~20250514183223.118), Debian LLD 
> 20.1.6 
>
> Unfortunately, I don't have any reproducer for this issue yet. 
>
> Downloadable assets: 
> disk image (non-bootable): 
> https://storage.googleapis.com/syzbot-assets/d900f083ada3/non_bootable_disk-7595b66a.raw.xz 
> vmlinux: 
> https://storage.googleapis.com/syzbot-assets/3332acf57c8d/vmlinux-7595b66a.xz 
> kernel image: 
> https://storage.googleapis.com/syzbot-assets/e83a48cfe09a/bzImage-7595b66a.xz 
>
> IMPORTANT: if you fix the issue, please add the following tag to the 
> commit: 
> Reported-by: syzbot+5e43fb...@...kaller.appspotmail.com 
>
> loop0: detected capacity change from 0 to 32768 
> bcachefs (loop0): starting version 1.7: mi_btree_bitmap 
> opts=metadata_checksum=crc64,data_checksum=none,compression=lz4,journal_flush_disabled,fsck,recovery_pass_last=set_may_go_rw,reconstruct_alloc,no_data_io 
>
> allowing incompatible features above 0.0: (unknown version) 
> features: 
> lz4,new_siphash,inline_data,new_extent_overwrite,btree_ptr_v2,new_varint,journal_no_flush,alloc_v2,extents_across_btree_nodes 
>
> bcachefs (loop0): Using encoding defined by superblock: utf8-12.1.0 
> bcachefs (loop0): recovering from clean shutdown, journal seq 10 
> bcachefs (loop0): Version upgrade required: 
> Version upgrade from 0.24: unwritten_extents to 1.7: mi_btree_bitmap 
> incomplete 
> Doing incompatible version upgrade from 0.24: unwritten_extents to 1.28: 
> inode_has_case_insensitive 
> running recovery passes: 
> check_allocations,check_alloc_info,check_lrus,check_btree_backpointers,check_backpointers_to_extents,check_extents_to_backpointers,check_alloc_to_lru_refs,bucket_gens_init,check_snapshot_trees,check_snapshots,check_subvols,check_subvol_children,delete_dead_snapshots,check_inodes,check_extents,check_indirect_extents,check_dirents,check_xattrs,check_root,check_unreachable_inodes,check_subvolume_structure,check_directory_structure,check_nlinks,check_rebalance_work,set_fs_needs_rebalance 
>
> bcachefs (loop0): dropping and reconstructing all alloc info 
> bcachefs (loop0): accounting_read... done 
> bcachefs (loop0): alloc_read... done 
> bcachefs (loop0): snapshots_read... done 
> bcachefs (loop0): check_allocations... done 
> bcachefs (loop0): going read-write 
> bcachefs (loop0): done starting filesystem 
> ------------[ cut here ]------------ 
> kernel BUG at fs/bcachefs/btree_journal_iter.c:139! 
> Oops: invalid opcode: 0000 [#1] SMP KASAN NOPTI 
> CPU: 0 UID: 0 PID: 5329 Comm: syz.0.0 Not tainted 
> 6.16.0-rc3-syzkaller-00044-g7595b66ae9de #0 PREEMPT(full) 
> Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 
> 1.16.3-debian-1.16.3-2~bpo12+1 04/01/2014 
> RIP: 0010:bch2_journal_keys_peek_prev_min+0x15e4/0x15f0 
> fs/bcachefs/btree_journal_iter.c:139 
> Code: b9 00 00 00 00 00 fc ff df 80 3c 08 00 74 08 48 89 df e8 ff 87 fe fd 
> 48 8b 1b e9 b6 fe ff ff e8 a2 5f 41 07 e8 1d 05 9b fd 90 <0f> 0b 66 2e 0f 
> 1f 84 00 00 00 00 00 90 90 90 90 90 90 90 90 90 90 
> RSP: 0018:ffffc9000d38f1a0 EFLAGS: 00010283 
> RAX: ffffffff84254803 RBX: ffffffffffffffff RCX: 0000000000100000 
> RDX: ffffc9000df5a000 RSI: 00000000000337b5 RDI: 00000000000337b6 
> RBP: ffffc9000d38f380 R08: 00090018ffffffff R09: 2000000000000000 
> R10: 0000000000000000 R11: 00090018ffffffff R12: ffffc9000d38f9b0 
> R13: dffffc0000000000 R14: 000000000000003b R15: ffff888052f00000 
> FS: 00007fe8791aa6c0(0000) GS:ffff88808d251000(0000) knlGS:0000000000000000 
> CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 
> CR2: 00007f1f90184000 CR3: 0000000043c47000 CR4: 0000000000352ef0 
> DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 
> DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400 
> Call Trace: 
> <TASK> 
> bch2_btree_journal_peek_prev fs/bcachefs/btree_iter.c:2172 [inline] 
> btree_trans_peek_prev_journal+0x259/0x3b0 fs/bcachefs/btree_iter.c:2186 
> __bch2_btree_iter_peek_prev fs/bcachefs/btree_iter.c:2560 [inline] 
> bch2_btree_iter_peek_prev_min+0x1439/0x5400 fs/bcachefs/btree_iter.c:2635 
> __bch2_resume_logged_op_finsert+0x7fc/0x2240 fs/bcachefs/io_misc.c:432 
> bch2_fcollapse_finsert+0x19b/0x250 fs/bcachefs/io_misc.c:536 
> bchfs_fcollapse_finsert+0x378/0x470 fs/bcachefs/fs-io.c:621 
> bch2_fallocate_dispatch+0x2a4/0x410 fs/bcachefs/fs-io.c:-1 
> vfs_fallocate+0x6a0/0x830 fs/open.c:341 
> ksys_fallocate fs/open.c:365 [inline] 
> __do_sys_fallocate fs/open.c:370 [inline] 
> __se_sys_fallocate fs/open.c:368 [inline] 
> __x64_sys_fallocate+0xc0/0x110 fs/open.c:368 
> do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline] 
> do_syscall_64+0xfa/0x3b0 arch/x86/entry/syscall_64.c:94 
> entry_SYSCALL_64_after_hwframe+0x77/0x7f 
> RIP: 0033:0x7fe87838e929 
> Code: ff ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 40 00 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 73 01 c3 48 c7 c1 a8 ff ff ff f7 d8 64 89 01 48 
> RSP: 002b:00007fe8791aa038 EFLAGS: 00000246 ORIG_RAX: 000000000000011d 
> RAX: ffffffffffffffda RBX: 00007fe8785b5fa0 RCX: 00007fe87838e929 
> RDX: 0000000000000000 RSI: 0000000000000020 RDI: 000000000000000a 
> RBP: 00007fe878410b39 R08: 0000000000000000 R09: 0000000000000000 
> R10: 0000000007000000 R11: 0000000000000246 R12: 0000000000000000 
> R13: 0000000000000000 R14: 00007fe8785b5fa0 R15: 00007ffc77682dc8 
> </TASK> 
> Modules linked in: 
> ---[ end trace 0000000000000000 ]--- 
> RIP: 0010:bch2_journal_keys_peek_prev_min+0x15e4/0x15f0 
> fs/bcachefs/btree_journal_iter.c:139 
> Code: b9 00 00 00 00 00 fc ff df 80 3c 08 00 74 08 48 89 df e8 ff 87 fe fd 
> 48 8b 1b e9 b6 fe ff ff e8 a2 5f 41 07 e8 1d 05 9b fd 90 <0f> 0b 66 2e 0f 
> 1f 84 00 00 00 00 00 90 90 90 90 90 90 90 90 90 90 
> RSP: 0018:ffffc9000d38f1a0 EFLAGS: 00010283 
> RAX: ffffffff84254803 RBX: ffffffffffffffff RCX: 0000000000100000 
> RDX: ffffc9000df5a000 RSI: 00000000000337b5 RDI: 00000000000337b6 
> RBP: ffffc9000d38f380 R08: 00090018ffffffff R09: 2000000000000000 
> R10: 0000000000000000 R11: 00090018ffffffff R12: ffffc9000d38f9b0 
> R13: dffffc0000000000 R14: 000000000000003b R15: ffff888052f00000 
> FS: 00007fe8791aa6c0(0000) GS:ffff88808d251000(0000) knlGS:0000000000000000 
> CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 
> CR2: 00007fe8783ec970 CR3: 0000000043c47000 CR4: 0000000000352ef0 
> DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 
> DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400 
>
>
> --- 
> 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 syzk...@...glegroups.com. 
>
> syzbot will keep track of this issue. See: 
> https://goo.gl/tpsmEJ#status for how to communicate with syzbot. 
>
> If the report is already addressed, let syzbot know by replying with: 
> #syz fix: exact-commit-title 
>
> If you want to overwrite report's subsystems, reply with: 
> #syz set subsystems: new-subsystem 
> (See the list of subsystem names on the web dashboard) 
>
> If the report is a duplicate of another one, reply with: 
> #syz dup: exact-subject-of-another-report 
>
> If you want to undo deduplication, reply with: 
> #syz undup 
>

Command #1:
This crash does not have a reproducer. I cannot test it.

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