[syzbot] [bcachefs?] KMSAN: uninit-value in bch2_btree_node_iter_init (2)

[syzbot] [bcachefs?] KMSAN: uninit-value in bch2_btree_node_iter_init (2)

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit:    3022e9d00ebe Merge tag 'sched_ext-for-6.12-rc7-fixes' of g..
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=162341a7980000
kernel config:  https://syzkaller.appspot.com/x/.config?x=dcca673786a14715
dashboard link: https://syzkaller.appspot.com/bug?extid=62f5ae3a10a9e97accd4
compiler:       Debian clang version 15.0.6, 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: https://storage.googleapis.com/syzbot-assets/937339c4ba17/disk-3022e9d0.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/23acd73c301b/vmlinux-3022e9d0.xz
kernel image: https://storage.googleapis.com/syzbot-assets/66d14471611f/bzImage-3022e9d0.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+62f5ae3a10a9e97accd4@syzkaller.appspotmail.com

=====================================================
BUG: KMSAN: uninit-value in bkey_cmp_p_or_unp fs/bcachefs/bset.h:287 [inline]
BUG: KMSAN: uninit-value in bkey_iter_cmp_p_or_unp fs/bcachefs/bset.h:400 [inline]
BUG: KMSAN: uninit-value in bch2_bset_search_linear fs/bcachefs/bset.c:1189 [inline]
BUG: KMSAN: uninit-value in bch2_btree_node_iter_init+0x319a/0x51a0 fs/bcachefs/bset.c:1334
 bkey_cmp_p_or_unp fs/bcachefs/bset.h:287 [inline]
 bkey_iter_cmp_p_or_unp fs/bcachefs/bset.h:400 [inline]
 bch2_bset_search_linear fs/bcachefs/bset.c:1189 [inline]
 bch2_btree_node_iter_init+0x319a/0x51a0 fs/bcachefs/bset.c:1334
 __btree_path_level_init fs/bcachefs/btree_iter.c:615 [inline]
 bch2_btree_path_level_init+0x821/0xc80 fs/bcachefs/btree_iter.c:635
 btree_path_lock_root fs/bcachefs/btree_iter.c:769 [inline]
 bch2_btree_path_traverse_one+0x379d/0x47b0 fs/bcachefs/btree_iter.c:1183
 bch2_btree_path_traverse fs/bcachefs/btree_iter.h:247 [inline]
 bch2_btree_iter_traverse+0xaf9/0x1020 fs/bcachefs/btree_iter.c:1880
 bch2_btree_node_update_key_get_iter+0x15c/0x9e0 fs/bcachefs/btree_update_interior.c:2481
 btree_node_write_work+0xb37/0x15a0 fs/bcachefs/btree_io.c:1874
 process_one_work kernel/workqueue.c:3229 [inline]
 process_scheduled_works+0xae0/0x1c40 kernel/workqueue.c:3310
 worker_thread+0xea7/0x14f0 kernel/workqueue.c:3391
 kthread+0x3e2/0x540 kernel/kthread.c:389
 ret_from_fork+0x6d/0x90 arch/x86/kernel/process.c:147
 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:244

Uninit was created at:
 ___kmalloc_large_node+0x22c/0x370 mm/slub.c:4219
 __kmalloc_large_node_noprof+0x3f/0x1e0 mm/slub.c:4236
 __do_kmalloc_node mm/slub.c:4252 [inline]
 __kmalloc_node_noprof+0x9d6/0xf50 mm/slub.c:4270
 __kvmalloc_node_noprof+0xc0/0x2d0 mm/util.c:658
 btree_bounce_alloc fs/bcachefs/btree_io.c:124 [inline]
 btree_node_sort+0x78a/0x1d30 fs/bcachefs/btree_io.c:323
 bch2_btree_post_write_cleanup+0x1b0/0xf20 fs/bcachefs/btree_io.c:2252
 bch2_btree_node_prep_for_write+0x494/0x720 fs/bcachefs/btree_trans_commit.c:93
 bch2_trans_lock_write+0x7ef/0xc00 fs/bcachefs/btree_trans_commit.c:129
 do_bch2_trans_commit fs/bcachefs/btree_trans_commit.c:896 [inline]
 __bch2_trans_commit+0x31c4/0xd190 fs/bcachefs/btree_trans_commit.c:1121
 bch2_trans_commit fs/bcachefs/btree_update.h:184 [inline]
 bch2_journal_replay+0x2e3d/0x4d30 fs/bcachefs/recovery.c:317
 bch2_run_recovery_pass fs/bcachefs/recovery_passes.c:185 [inline]
 bch2_run_recovery_passes+0xaf9/0xf80 fs/bcachefs/recovery_passes.c:238
 bch2_fs_recovery+0x447b/0x5b00 fs/bcachefs/recovery.c:861
 bch2_fs_start+0x7b2/0xbd0 fs/bcachefs/super.c:1036
 bch2_fs_get_tree+0x13ea/0x22d0 fs/bcachefs/fs.c:2170
 vfs_get_tree+0xb1/0x5a0 fs/super.c:1814
 do_new_mount+0x71f/0x15e0 fs/namespace.c:3507
 path_mount+0x742/0x1f10 fs/namespace.c:3834
 do_mount fs/namespace.c:3847 [inline]
 __do_sys_mount fs/namespace.c:4057 [inline]
 __se_sys_mount+0x722/0x810 fs/namespace.c:4034
 __ia32_sys_mount+0xe3/0x150 fs/namespace.c:4034
 ia32_sys_call+0x2530/0x40d0 arch/x86/include/generated/asm/syscalls_32.h:22
 do_syscall_32_irqs_on arch/x86/entry/common.c:165 [inline]
 __do_fast_syscall_32+0xb0/0x110 arch/x86/entry/common.c:386
 do_fast_syscall_32+0x38/0x80 arch/x86/entry/common.c:411
 do_SYSENTER_32+0x1f/0x30 arch/x86/entry/common.c:449
 entry_SYSENTER_compat_after_hwframe+0x84/0x8e

CPU: 0 UID: 0 PID: 43 Comm: kworker/0:1H Not tainted 6.12.0-rc7-syzkaller-00012-g3022e9d00ebe #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/30/2024
Workqueue: bcachefs_btree_io btree_node_write_work
=====================================================


---
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Re: [syzbot] [bcachefs?] KMSAN: uninit-value in bch2_btree_node_iter_init (2)

[Piotr Zalewski]

Hi, all

This seems to be the proper way to fix this?:

diff --git a/fs/bcachefs/btree_io.c b/fs/bcachefs/btree_io.c
index 89a42ee81e5c..f92a3fb946de 100644
--- a/fs/bcachefs/btree_io.c
+++ b/fs/bcachefs/btree_io.c
@@ -324,6 +324,7 @@ static void btree_node_sort(struct bch_fs *c, struct btree *b,
 	start_time = local_clock();
 
 	u64s = bch2_sort_keys(out->keys.start, &sort_iter.iter);
+	memset((out->keys.start + u64s), 0, bytes - sizeof(struct btree_node) - u64s * sizeof(u64));
 
 	out->keys.u64s = cpu_to_le16(u64s);
 

Re: [syzbot] [bcachefs?] KMSAN: uninit-value in bch2_btree_node_iter_init (2)

[Kent Overstreet]

On Sun, Nov 17, 2024 at 11:51:39PM +0000, Piotr Zalewski wrote:
> Hi, all
> 
> This seems to be the proper way to fix this?:
> 
> diff --git a/fs/bcachefs/btree_io.c b/fs/bcachefs/btree_io.c
> index 89a42ee81e5c..f92a3fb946de 100644
> --- a/fs/bcachefs/btree_io.c
> +++ b/fs/bcachefs/btree_io.c
> @@ -324,6 +324,7 @@ static void btree_node_sort(struct bch_fs *c, struct btree *b,
>  	start_time = local_clock();
>  
>  	u64s = bch2_sort_keys(out->keys.start, &sort_iter.iter);
> +	memset((out->keys.start + u64s), 0, bytes - sizeof(struct btree_node) - u64s * sizeof(u64));
>  
>  	out->keys.u64s = cpu_to_le16(u64s);

Did you do any analysis you can share?

It seems like zeroing out the rest of the buffer shouldn't be necessary:
we do that at write time, where it really is necessary, otherwise we
shouldn't be accessing parts of the buffer that don't have valid keys in
them.

varint_decode_fast, used for inodes, does do reads (that aren't used) up
to 7 bytes past the valid data, so it could be needed if we were seeing
kmsan splats there - but this is bkey comparison, so something fishy
seems to be going on.

Re: [syzbot] [bcachefs?] KMSAN: uninit-value in bch2_btree_node_iter_init (2)

[syzbot]

syzbot has found a reproducer for the following issue on:

HEAD commit:    9f16d5e6f220 Merge tag 'for-linus' of git://git.kernel.org..
git tree:       upstream
console+strace: https://syzkaller.appspot.com/x/log.txt?x=17ba8778580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=197de11c5dba9f21
dashboard link: https://syzkaller.appspot.com/bug?extid=62f5ae3a10a9e97accd4
compiler:       Debian clang version 15.0.6, GNU ld (GNU Binutils for Debian) 2.40
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=10e219c0580000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=1483d75f980000

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/d544df92b8b9/disk-9f16d5e6.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/cfb277b7148a/vmlinux-9f16d5e6.xz
kernel image: https://storage.googleapis.com/syzbot-assets/b9aeb9fe1f9d/bzImage-9f16d5e6.xz
mounted in repro: https://storage.googleapis.com/syzbot-assets/623571bff0e8/mount_0.gz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+62f5ae3a10a9e97accd4@syzkaller.appspotmail.com

bucket 0:127 gen 0 has wrong data_type: got free, should be sb, fixing
bucket 0:127 gen 0 data type sb has wrong dirty_sectors: got 0, should be 256, fixing
 done
bcachefs (loop0): going read-write
bcachefs (loop0): journal_replay...
=====================================================
BUG: KMSAN: uninit-value in bkey_cmp_p_or_unp fs/bcachefs/bset.h:287 [inline]
BUG: KMSAN: uninit-value in bkey_iter_cmp_p_or_unp fs/bcachefs/bset.h:400 [inline]
BUG: KMSAN: uninit-value in bch2_bset_search_linear fs/bcachefs/bset.c:1189 [inline]
BUG: KMSAN: uninit-value in bch2_btree_node_iter_init+0x319a/0x51a0 fs/bcachefs/bset.c:1334
 bkey_cmp_p_or_unp fs/bcachefs/bset.h:287 [inline]
 bkey_iter_cmp_p_or_unp fs/bcachefs/bset.h:400 [inline]
 bch2_bset_search_linear fs/bcachefs/bset.c:1189 [inline]
 bch2_btree_node_iter_init+0x319a/0x51a0 fs/bcachefs/bset.c:1334
 __btree_path_level_init fs/bcachefs/btree_iter.c:615 [inline]
 bch2_btree_path_level_init+0x821/0xc80 fs/bcachefs/btree_iter.c:635
 btree_path_lock_root fs/bcachefs/btree_iter.c:769 [inline]
 bch2_btree_path_traverse_one+0x379d/0x47b0 fs/bcachefs/btree_iter.c:1183
 bch2_btree_path_traverse fs/bcachefs/btree_iter.h:247 [inline]
 flush_new_cached_update+0x296/0xad0 fs/bcachefs/btree_update.c:358
 bch2_trans_update_by_path+0x2493/0x2820 fs/bcachefs/btree_update.c:466
 bch2_trans_update+0xf45/0x2410 fs/bcachefs/btree_update.c:546
 bch2_journal_replay_key+0xe14/0x13f0 fs/bcachefs/recovery.c:232
 bch2_journal_replay+0x2d2e/0x4d30 fs/bcachefs/recovery.c:317
 bch2_run_recovery_pass fs/bcachefs/recovery_passes.c:191 [inline]
 bch2_run_recovery_passes+0xaf9/0xf80 fs/bcachefs/recovery_passes.c:244
 bch2_fs_recovery+0x447b/0x5b00 fs/bcachefs/recovery.c:861
 bch2_fs_start+0x7b2/0xbd0 fs/bcachefs/super.c:1037
 bch2_fs_get_tree+0x13ea/0x22d0 fs/bcachefs/fs.c:2170
 vfs_get_tree+0xb1/0x5a0 fs/super.c:1814
 do_new_mount+0x71f/0x15e0 fs/namespace.c:3507
 path_mount+0x742/0x1f10 fs/namespace.c:3834
 do_mount fs/namespace.c:3847 [inline]
 __do_sys_mount fs/namespace.c:4057 [inline]
 __se_sys_mount+0x722/0x810 fs/namespace.c:4034
 __x64_sys_mount+0xe4/0x150 fs/namespace.c:4034
 x64_sys_call+0x39bf/0x3c30 arch/x86/include/generated/asm/syscalls_64.h:166
 do_syscall_x64 arch/x86/entry/common.c:52 [inline]
 do_syscall_64+0xcd/0x1e0 arch/x86/entry/common.c:83
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

Uninit was created at:
 ___kmalloc_large_node+0x22c/0x370 mm/slub.c:4219
 __kmalloc_large_node_noprof+0x3f/0x1e0 mm/slub.c:4236
 __do_kmalloc_node mm/slub.c:4252 [inline]
 __kmalloc_node_noprof+0x9d6/0xf50 mm/slub.c:4270
 __kvmalloc_node_noprof+0xc0/0x2d0 mm/util.c:658
 btree_node_data_alloc fs/bcachefs/btree_cache.c:153 [inline]
 __bch2_btree_node_mem_alloc+0x2be/0xa80 fs/bcachefs/btree_cache.c:198
 bch2_fs_btree_cache_init+0x4e4/0xb50 fs/bcachefs/btree_cache.c:653
 bch2_fs_alloc fs/bcachefs/super.c:917 [inline]
 bch2_fs_open+0x4d3a/0x5b40 fs/bcachefs/super.c:2065
 bch2_fs_get_tree+0x983/0x22d0 fs/bcachefs/fs.c:2157
 vfs_get_tree+0xb1/0x5a0 fs/super.c:1814
 do_new_mount+0x71f/0x15e0 fs/namespace.c:3507
 path_mount+0x742/0x1f10 fs/namespace.c:3834
 do_mount fs/namespace.c:3847 [inline]
 __do_sys_mount fs/namespace.c:4057 [inline]
 __se_sys_mount+0x722/0x810 fs/namespace.c:4034
 __x64_sys_mount+0xe4/0x150 fs/namespace.c:4034
 x64_sys_call+0x39bf/0x3c30 arch/x86/include/generated/asm/syscalls_64.h:166
 do_syscall_x64 arch/x86/entry/common.c:52 [inline]
 do_syscall_64+0xcd/0x1e0 arch/x86/entry/common.c:83
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

CPU: 1 UID: 0 PID: 5805 Comm: syz-executor322 Not tainted 6.12.0-syzkaller-09073-g9f16d5e6f220 #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 09/13/2024
=====================================================


---
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Re: [syzbot]

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***

Subject: 
Author: kent.overstreet@linux.dev

#syz fix bcachefs: Disable asm memcpys when kmsan enabled