Re: [PATCH 1/2] ext4: fail ext4_iget if special inode unallocated

[Baokun Li]

On 2023/1/6 22:28, Jan Kara wrote:
> On Fri 06-01-23 18:47:05, Baokun Li wrote:
> > In ext4_fill_super(), EXT4_ORPHAN_FS flag is cleared after
> > ext4_orphan_cleanup() is executed. Therefore, when __ext4_iget() is
> > called to get an inode whose i_nlink is 0 when the flag exists, no error
> > is returned. If the inode is a special inode, a null pointer dereference
> > may occur. If the value of i_nlink is 0 for any inodes (except boot loader
> > inodes) got by using the EXT4_IGET_SPECIAL flag, the current file system
> > is corrupted. Therefore, make the ext4_iget() function return an error if
> > it gets such an abnormal special inode.
> >
> > Link: https://bugzilla.kernel.org/show_bug.cgi?id=199179
> > Link: https://bugzilla.kernel.org/show_bug.cgi?id=216541
> > Link: https://bugzilla.kernel.org/show_bug.cgi?id=216539
> > Reported-by: Luís Henriques <lhenriques@xxxxxxx>
> > Suggested-by: Theodore Ts'o <tytso@xxxxxxx>
> > Signed-off-by: Baokun Li <libaokun1@xxxxxxxxxx>
> Thanks for the patch! A few comments below.
>
> > diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
> > index 9d9f414f99fe..3f7cfa91ba89 100644
> > --- a/fs/ext4/inode.c
> > +++ b/fs/ext4/inode.c
> > @@ -4872,13 +4872,6 @@ struct inode *__ext4_iget(struct super_block *sb, unsigned long ino,
> >   		goto bad_inode;
> >   	raw_inode = ext4_raw_inode(&iloc);
> >   
> > -	if ((ino == EXT4_ROOT_INO) && (raw_inode->i_links_count == 0)) {
> > -		ext4_error_inode(inode, function, line, 0,
> > -				 "iget: root inode unallocated");
> > -		ret = -EFSCORRUPTED;
> > -		goto bad_inode;
> > -	}
> > -
> >   	if ((flags & EXT4_IGET_HANDLE) &&
> >   	    (raw_inode->i_links_count == 0) && (raw_inode->i_mode == 0)) {
> >   		ret = -ESTALE;
> > @@ -4951,10 +4944,13 @@ struct inode *__ext4_iget(struct super_block *sb, unsigned long ino,
> >   	 * NeilBrown 1999oct15
> >   	 */
> >   	if (inode->i_nlink == 0) {
> > -		if ((inode->i_mode == 0 ||
> > +		if ((inode->i_mode == 0 || (flags & EXT4_IGET_SPECIAL) ||
> 					   ^ extra parenthesis here  ^
Indeed, I'll remove the extra parenthesis.
> >   		     !(EXT4_SB(inode->i_sb)->s_mount_state & EXT4_ORPHAN_FS)) &&
> >   		    ino != EXT4_BOOT_LOADER_INO) {
> >   			/* this inode is deleted */
> > +			if (flags & EXT4_IGET_SPECIAL)
> > +				ext4_error_inode(inode, function, line, 0,
> > +						 "iget: special inode unallocated");
> I think it would be better to return -EFSCORRUPTED and not -ESTALE in this
> case.
Totally agree! For special inode, -EFSCORRUPTED is more reasonable.
> >   			ret = -ESTALE;
> >   			goto bad_inode;
> >   		}
> Otherwise the patch looks good to me.
>
> 									Honza
Thank you very much for your review！
I will send a patch V2 with the changes suggested by you.

--
With Best Regards,
Baokun Li
.