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References: <20230731010104.1781335-1-zhangshida@kylinos.cn> <20230731154133.GA11332@frogsfrogsfrogs>
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From:   Stephen Zhang <starzhangzsd@gmail.com>
Date:   Tue, 1 Aug 2023 10:26:55 +0800
Message-ID: <CANubcdVMdisPOR=VD4mLyiQru4oPOZ_0oDSZXRYOu6ynTji2vA@mail.gmail.com>
Subject: Re: [PATCH v2] ext4: Fix rec_len verify error
To:     "Darrick J. Wong" <djwong@kernel.org>
Cc:     tytso@mit.edu, adilger.kernel@dilger.ca,
        linux-ext4@vger.kernel.org, linux-kernel@vger.kernel.org,
        zhangshida@kylinos.cn
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Darrick J. Wong <djwong@kernel.org> =E4=BA=8E2023=E5=B9=B47=E6=9C=8831=E6=
=97=A5=E5=91=A8=E4=B8=80 23:41=E5=86=99=E9=81=93=EF=BC=9A
>
> On Mon, Jul 31, 2023 at 09:01:04AM +0800, zhangshida wrote:
> > From: Shida Zhang <zhangshida@kylinos.cn>
> >
> > With the configuration PAGE_SIZE 64k and filesystem blocksize 64k,
> > a problem occurred when more than 13 million files were directly create=
d
> > under a directory:
> >
> > EXT4-fs error (device xx): ext4_dx_csum_set:492: inode #xxxx: comm xxxx=
x: dir seems corrupt?  Run e2fsck -D.
> > EXT4-fs error (device xx): ext4_dx_csum_verify:463: inode #xxxx: comm x=
xxxx: dir seems corrupt?  Run e2fsck -D.
> > EXT4-fs error (device xx): dx_probe:856: inode #xxxx: block 8188: comm =
xxxxx: Directory index failed checksum
> >
> > When enough files are created, the fake_dirent->reclen will be 0xffff.
> > it doesn't equal to the blocksize 65536, i.e. 0x10000.
> >
> > But it is not the same condition when blocksize equals to 4k.
> > when enough file are created, the fake_dirent->reclen will be 0x1000.
> > it equals to the blocksize 4k, i.e. 0x1000.
> >
> > The problem seems to be related to the limitation of the 16-bit field
> > when the blocksize is set to 64k. To address this, Modify the check so
> > as to handle it properly.
>
> urughghahrhrhr<shudder>
>
> Sorry that I missed that rec_len is an encoded number, not a plain le16
> integer...
>

Yep, that's really a point that is easy to forget...

> > Signed-off-by: Shida Zhang <zhangshida@kylinos.cn>
> > ---
> > v1->v2:
> >   Use a better way to check the condition, as suggested by Andreas.
> >
> >  fs/ext4/namei.c | 3 ++-
> >  1 file changed, 2 insertions(+), 1 deletion(-)
> >
> > diff --git a/fs/ext4/namei.c b/fs/ext4/namei.c
> > index 0caf6c730ce3..fffed95f8531 100644
> > --- a/fs/ext4/namei.c
> > +++ b/fs/ext4/namei.c
> > @@ -445,8 +445,9 @@ static struct dx_countlimit *get_dx_countlimit(stru=
ct inode *inode,
> >       struct ext4_dir_entry *dp;
> >       struct dx_root_info *root;
> >       int count_offset;
> > +     int blocksize =3D EXT4_BLOCK_SIZE(inode->i_sb);
> >
> > -     if (le16_to_cpu(dirent->rec_len) =3D=3D EXT4_BLOCK_SIZE(inode->i_=
sb))
> > +     if (ext4_rec_len_from_disk(dirent->rec_len, blocksize) =3D=3D blo=
cksize)
> >               count_offset =3D 8;
> >       else if (le16_to_cpu(dirent->rec_len) =3D=3D 12) {
>
> ...but what about all the other le16_to_cpu(ext4_dir_entry{,_2}.rec_len)
> accesses in this file?  Don't those also need to be converted to
> ext4_rec_len_from_disk calls?
>
> Also,
> Fixes: dbe89444042ab ("ext4: Calculate and verify checksums for htree nod=
es")
>

Thanks for your suggestion, I will try to add all the other conversion
in this file for the next v3.

Cheers,
Shida


> --D
>
> >               dp =3D (struct ext4_dir_entry *)(((void *)dirent) + 12);
> > --
> > 2.27.0
> >