linux-kernel - Re: [PATCH v1] bcachefs: set freespace inited to false if trans_mark_dev

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Message-ID: <b22xc632ptvw3jtkyp5yqj6lxpnbdwlmqxekafuunjxxsaup7n@jrybxzaqj4li>
Date: Sun, 20 Oct 2024 19:23:00 -0400
From: Kent Overstreet <kent.overstreet@...ux.dev>
To: Piotr Zalewski <pZ010001011111@...ton.me>
Cc: linux-bcachefs@...r.kernel.org, linux-kernel@...r.kernel.org, 
	skhan@...uxfoundation.org, syzbot+2b6a17991a6af64f9489@...kaller.appspotmail.com
Subject: Re: [PATCH v1] bcachefs: set freespace inited to false if
 trans_mark_dev_sbs fails

On Sun, Oct 20, 2024 at 05:08:45PM +0000, Piotr Zalewski wrote:
> In bch2_fs_initialize if bch2_trans_mark_dev_sbs fails, set freespace
> initialized bits to 0 in member's flags and update member cached version
> for each device. bch2_trans_mark_dev_sbs fails just before freespace
> init which can left freespace init bits set to true erroneously which later
> can indirectly trigger BUG condition in bch2_bucket_alloc_freelist[1].

Err...

freespace_initialized shouldn't even be set at this point, it's set
later, in bch2_fs_freespace_init(), naturally.

So - syzbot is feeding us garbage, heh. BCH_MEMBER_FREESPACE_INITIALIZED
should be false on a non initialized filesystem.

So we actually should be unconditially clearing it (sanitizing our
input) at the top of bch2_fs_initialize().

> 
> [1] https://syzkaller.appspot.com/bug?extid=2b6a17991a6af64f9489
> 
> Reported-by: syzbot+2b6a17991a6af64f9489@...kaller.appspotmail.com
> Closes: https://syzkaller.appspot.com/bug?extid=2b6a17991a6af64f9489
> Fixes: bbe682c76789 ("bcachefs: Ensure devices are always correctly initialized")
> Signed-off-by: Piotr Zalewski <pZ010001011111@...ton.me>
> ---
>  fs/bcachefs/recovery.c | 12 +++++++++++-
>  1 file changed, 11 insertions(+), 1 deletion(-)
> 
> diff --git a/fs/bcachefs/recovery.c b/fs/bcachefs/recovery.c
> index 67bba156cce9..bcec79122f65 100644
> --- a/fs/bcachefs/recovery.c
> +++ b/fs/bcachefs/recovery.c
> @@ -1031,6 +1031,7 @@ int bch2_fs_initialize(struct bch_fs *c)
>  	struct bkey_inode_buf packed_inode;
>  	struct qstr lostfound = QSTR("lost+found");
>  	int ret;
> +	struct bch_member *m;
>  
>  	bch_notice(c, "initializing new filesystem");
>  	set_bit(BCH_FS_new_fs, &c->flags);
> @@ -1086,8 +1087,17 @@ int bch2_fs_initialize(struct bch_fs *c)
>  	bch_verbose(c, "marking superblocks");
>  	ret = bch2_trans_mark_dev_sbs(c);
>  	bch_err_msg(c, ret, "marking superblocks");
> -	if (ret)
> +	if (ret) {
> +		mutex_lock(&c->sb_lock);
> +		for_each_member_device(c, ca) {
> +			m = bch2_members_v2_get_mut(c->disk_sb.sb, ca->dev_idx);
> +			SET_BCH_MEMBER_FREESPACE_INITIALIZED(m, false);
> +			ca->mi = bch2_mi_to_cpu(m);
> +		}
> +		mutex_unlock(&c->sb_lock);
> +
>  		goto err;
> +	}
>  
>  	for_each_online_member(c, ca)
>  		ca->new_fs_bucket_idx = 0;
> -- 
> 2.47.0
> 
>