Re: [PATCH] ext4: fix uninitialized ratelimit_state->lock access in __ext4_fill_super()

[Jan Kara]

On Tue 02-01-24 21:37:30, Baokun Li wrote:
> In the following concurrency we will access the uninitialized rs->lock:
> 
> ext4_fill_super
>   ext4_register_sysfs
>    // sysfs registered msg_ratelimit_interval_ms
>                              // Other processes modify rs->interval to
>                              // non-zero via msg_ratelimit_interval_ms
>   ext4_orphan_cleanup
>     ext4_msg(sb, KERN_INFO, "Errors on filesystem, "
>       __ext4_msg
>         ___ratelimit(&(EXT4_SB(sb)->s_msg_ratelimit_state)
>           if (!rs->interval)  // do nothing if interval is 0
>             return 1;
>           raw_spin_trylock_irqsave(&rs->lock, flags)
>             raw_spin_trylock(lock)
>               _raw_spin_trylock
>                 __raw_spin_trylock
>                   spin_acquire(&lock->dep_map, 0, 1, _RET_IP_)
>                     lock_acquire
>                       __lock_acquire
>                         register_lock_class
>                           assign_lock_key
>                             dump_stack();
>   ratelimit_state_init(&sbi->s_msg_ratelimit_state, 5 * HZ, 10);
>     raw_spin_lock_init(&rs->lock);
>     // init rs->lock here
> 
> and get the following dump_stack:
> 
> =========================================================
> INFO: trying to register non-static key.
> The code is fine but needs lockdep annotation, or maybe
> you didn't initialize this object before use?
> turning off the locking correctness validator.
> CPU: 12 PID: 753 Comm: mount Tainted: G E 6.7.0-rc6-next-20231222 #504
> [...]
> Call Trace:
>  dump_stack_lvl+0xc5/0x170
>  dump_stack+0x18/0x30
>  register_lock_class+0x740/0x7c0
>  __lock_acquire+0x69/0x13a0
>  lock_acquire+0x120/0x450
>  _raw_spin_trylock+0x98/0xd0
>  ___ratelimit+0xf6/0x220
>  __ext4_msg+0x7f/0x160 [ext4]
>  ext4_orphan_cleanup+0x665/0x740 [ext4]
>  __ext4_fill_super+0x21ea/0x2b10 [ext4]
>  ext4_fill_super+0x14d/0x360 [ext4]
> [...]
> =========================================================
> 
> Normally interval is 0 until s_msg_ratelimit_state is initialized, so
> ___ratelimit() does nothing. But registering sysfs precedes initializing
> rs->lock, so it is possible to change rs->interval to a non-zero value
> via the msg_ratelimit_interval_ms interface of sysfs while rs->lock is
> uninitialized, and then a call to ext4_msg triggers the problem by
> accessing an uninitialized rs->lock. Therefore register sysfs after all
> initializations are complete to avoid such problems.
> 
> Signed-off-by: Baokun Li <libaokun1@xxxxxxxxxx>

Looks good to me. Feel free to add:

Reviewed-by: Jan Kara <jack@xxxxxxx>

								Honza

> ---
>  fs/ext4/super.c | 22 ++++++++++------------
>  1 file changed, 10 insertions(+), 12 deletions(-)
> 
> diff --git a/fs/ext4/super.c b/fs/ext4/super.c
> index 0980845c8b8f..1db23b0e8a4f 100644
> --- a/fs/ext4/super.c
> +++ b/fs/ext4/super.c
> @@ -5564,19 +5564,15 @@ static int __ext4_fill_super(struct fs_context *fc, struct super_block *sb)
>  	if (err)
>  		goto failed_mount6;
>  
> -	err = ext4_register_sysfs(sb);
> -	if (err)
> -		goto failed_mount7;
> -
>  	err = ext4_init_orphan_info(sb);
>  	if (err)
> -		goto failed_mount8;
> +		goto failed_mount7;
>  #ifdef CONFIG_QUOTA
>  	/* Enable quota usage during mount. */
>  	if (ext4_has_feature_quota(sb) && !sb_rdonly(sb)) {
>  		err = ext4_enable_quotas(sb);
>  		if (err)
> -			goto failed_mount9;
> +			goto failed_mount8;
>  	}
>  #endif  /* CONFIG_QUOTA */
>  
> @@ -5602,7 +5598,7 @@ static int __ext4_fill_super(struct fs_context *fc, struct super_block *sb)
>  		ext4_msg(sb, KERN_INFO, "recovery complete");
>  		err = ext4_mark_recovery_complete(sb, es);
>  		if (err)
> -			goto failed_mount10;
> +			goto failed_mount9;
>  	}
>  
>  	if (test_opt(sb, DISCARD) && !bdev_max_discard_sectors(sb->s_bdev))
> @@ -5619,15 +5615,17 @@ static int __ext4_fill_super(struct fs_context *fc, struct super_block *sb)
>  	atomic_set(&sbi->s_warning_count, 0);
>  	atomic_set(&sbi->s_msg_count, 0);
>  
> +	/* Register sysfs after all initializations are complete. */
> +	err = ext4_register_sysfs(sb);
> +	if (err)
> +		goto failed_mount9;
> +
>  	return 0;
>  
> -failed_mount10:
> +failed_mount9:
>  	ext4_quotas_off(sb, EXT4_MAXQUOTAS);
> -failed_mount9: __maybe_unused
> +failed_mount8: __maybe_unused
>  	ext4_release_orphan_info(sb);
> -failed_mount8:
> -	ext4_unregister_sysfs(sb);
> -	kobject_put(&sbi->s_kobj);
>  failed_mount7:
>  	ext4_unregister_li_request(sb);
>  failed_mount6:
> -- 
> 2.31.1
> 
-- 
Jan Kara <jack@xxxxxxxx>
SUSE Labs, CR