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Message-ID: <5ef2e2838b0d07d3f05edd2a2a169e7647782de5.camel@ibm.com>
Date: Thu, 24 Jul 2025 19:49:50 +0000
From: Viacheslav Dubeyko <Slava.Dubeyko@....com>
To: "penguin-kernel@...ove.SAKURA.ne.jp" <penguin-kernel@...ove.SAKURA.ne.jp>,
"willy@...radead.org" <willy@...radead.org>
CC: "glaubitz@...sik.fu-berlin.de" <glaubitz@...sik.fu-berlin.de>,
"frank.li@...o.com" <frank.li@...o.com>,
"slava@...eyko.com"
<slava@...eyko.com>,
"linux-fsdevel@...r.kernel.org"
<linux-fsdevel@...r.kernel.org>,
"linux-kernel@...r.kernel.org"
<linux-kernel@...r.kernel.org>,
"akpm@...ux-foundation.org"
<akpm@...ux-foundation.org>
Subject: RE: [PATCH v3] hfs: remove BUG() from
hfs_release_folio()/hfs_test_inode()/hfs_write_inode()
On Thu, 2025-07-24 at 15:55 +0900, Tetsuo Handa wrote:
> Then, something like below change?
>
> --- a/fs/hfs/inode.c
> +++ b/fs/hfs/inode.c
> @@ -318,6 +318,9 @@ static int hfs_read_inode(struct inode *inode, void *data)
> struct hfs_iget_data *idata = data;
> struct hfs_sb_info *hsb = HFS_SB(inode->i_sb);
> hfs_cat_rec *rec;
> + /* https://developer.apple.com/library/archive/technotes/tn/tn1150.html#CNID */
We already have all declarations in hfs.h:
/* Some special File ID numbers */
#define HFS_POR_CNID 1 /* Parent Of the Root */
#define HFS_ROOT_CNID 2 /* ROOT directory */
#define HFS_EXT_CNID 3 /* EXTents B-tree */
#define HFS_CAT_CNID 4 /* CATalog B-tree */
#define HFS_BAD_CNID 5 /* BAD blocks file */
#define HFS_ALLOC_CNID 6 /* ALLOCation file (HFS+) */
#define HFS_START_CNID 7 /* STARTup file (HFS+) */
#define HFS_ATTR_CNID 8 /* ATTRibutes file (HFS+) */
#define HFS_EXCH_CNID 15 /* ExchangeFiles temp id */
#define HFS_FIRSTUSER_CNID 16
So, adding the link here doesn't make any sense.
> + static const u16 bad_cnid_list = (1 << 0) | (1 << 6) | (1 << 7) | (1 << 8) |
> + (1 << 9) | (1 << 10) | (1 << 11) | (1 << 12) | (1 << 13);
I don't see any sense to introduce flags here. First of all, please, don't use
hardcoded values but you should use declared constants from hfs.h (for example,
HFS_EXT_CNID instead of 3). Secondly, you can simply compare the i_ino with
constants, for example:
bool is_inode_id_invalid(u64 ino) {
switch (inode->i_ino) {
case HFS_EXT_CNID:
...
return true;
}
return false;
}
Thirdly, you can introduce an inline function that can do such check. And it
make sense to introduce constant for the case of zero value.
Why have you missed HFS_EXT_CNID, HFS_CAT_CNID? These values cannot used in
hfs_read_inode().
>
> HFS_I(inode)->flags = 0;
> HFS_I(inode)->rsrc_inode = NULL;
> @@ -358,6 +361,8 @@ static int hfs_read_inode(struct inode *inode, void *data)
> inode->i_op = &hfs_file_inode_operations;
> inode->i_fop = &hfs_file_operations;
> inode->i_mapping->a_ops = &hfs_aops;
> + if (inode->i_ino < HFS_FIRSTUSER_CNID && ((1U << inode->i_ino) & bad_cnid_list))
> + make_bad_inode(inode);
It looks pretty complicated. You can simply use one above-mentioned function
with the check:
if (is_inode_id_invalid(be32_to_cpu(rec->dir.DirID)))
<goto to make bad inode>
We can simply check the the inode ID in the beginning of the whole action:
<Make the check here>
inode->i_ino = be32_to_cpu(rec->file.FlNum);
inode->i_mode = S_IRUGO | S_IXUGO;
if (!(rec->file.Flags & HFS_FIL_LOCK))
inode->i_mode |= S_IWUGO;
inode->i_mode &= ~hsb->s_file_umask;
inode->i_mode |= S_IFREG;
inode_set_mtime_to_ts(inode,
inode_set_atime_to_ts(inode,
inode_set_ctime_to_ts(inode, hfs_m_to_utime(rec->file.MdDat))));
inode->i_op = &hfs_file_inode_operations;
inode->i_fop = &hfs_file_operations;
inode->i_mapping->a_ops = &hfs_aops;
It doesn't make any sense to construct inode if we will make in bad inode,
finally. Don't waste computational power. :)
> break;
> case HFS_CDR_DIR:
> inode->i_ino = be32_to_cpu(rec->dir.DirID);
> @@ -368,6 +373,8 @@ static int hfs_read_inode(struct inode *inode, void *data)
> inode_set_atime_to_ts(inode, inode_set_ctime_to_ts(inode, hfs_m_to_utime(rec->dir.MdDat))));
> inode->i_op = &hfs_dir_inode_operations;
> inode->i_fop = &hfs_dir_operations;
> + if (inode->i_ino < HFS_FIRSTUSER_CNID && ((1U << inode->i_ino) & bad_cnid_list))
> + make_bad_inode(inode);
We already have make_bad_inode(inode) as default action. So, simply jump there.
> break;
> default:
> make_bad_inode(inode);
>
>
>
> But I can't be convinced that above change is sufficient, for if I do
>
> + static u8 serial;
> + if (inode->i_ino < HFS_FIRSTUSER_CNID && ((1U << inode->i_ino) & bad_cnid_list))
> + inode->i_ino = (serial++) % 16;
I don't see the point in flags introduction. It makes logic very complicated.
>
> instead of
>
> + if (inode->i_ino < HFS_FIRSTUSER_CNID && ((1U << inode->i_ino) & bad_cnid_list))
> + make_bad_inode(inode);
>
> , the reproducer still hits BUG() for 0, 1, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14 and 15
> because hfs_write_inode() handles only 2, 3 and 4.
>
How can we go into hfs_write_inode() if we created the bad inode for invalid
inode ID? How is it possible?
Thanks,
Slava.
> if (inode->i_ino < HFS_FIRSTUSER_CNID) {
> switch (inode->i_ino) {
> case HFS_ROOT_CNID:
> break;
> case HFS_EXT_CNID:
> hfs_btree_write(HFS_SB(inode->i_sb)->ext_tree);
> return 0;
> case HFS_CAT_CNID:
> hfs_btree_write(HFS_SB(inode->i_sb)->cat_tree);
> return 0;
> default:
> BUG();
> return -EIO;
> }
> }
>
> Unless this is because I'm modifying in-kernel memory than filesystem image,
> we will have to remove BUG() line.
>
> On 2025/07/24 3:43, Viacheslav Dubeyko wrote:
> > This could be defined in Catalog File (maybe not). I didn't find anything
> > related to this in HFS specification.
>
> https://developer.apple.com/library/archive/technotes/tn/tn1150.html#CNID
> says "the CNID of zero is never used and serves as a nil value." That is,
> I think we can reject inode->i_ino == 0 case.
>
> But I'm not sure for other values up to 15, expect values noted as "introduced
> with HFS Plus". We could filter values in bad_cnid_list bitmap, but filtering
> undefined values might not be sufficient for preserving BUG() line.
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