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

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Message-ID: <zBWzq5qj3_X8s9g2hXy8ZwvGLcPoBLQJRtb4E85aZlFyDOYvqKsHT8xzaLsLssWvRhdP7NkhMxrV8lhG8UXJxSXH1z6qjudgvj6VIcDQPV4=@proton.me>
Date: Mon, 21 Oct 2024 08:05:23 +0000
From: Piotr Zalewski <pZ010001011111@...ton.me>
To: Kent Overstreet <kent.overstreet@...ux.dev>
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

Hi Kent,

On Monday, October 21st, 2024 at 1:23 AM, Kent Overstreet <kent.overstreet@...ux.dev> wrote:

> 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().

Initially I added it at the beginning of bch2_fs_initialize. I changed it
to here since then the error triggered is ENOSPC_disk_reservation instead
of EIO. I thought that it's somewhat important to retain the error so moved
it to the if statement.

I will move it to the sb_lock at the top. After syzbot tests it I will send
v2.

> > [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

Best regards, Piotr Zalewski