Re: linux-next ext4 inode size 128 corrupted

[Hugh Dickins]

On Tue, 18 Jul 2023, Jeff Layton wrote:
> On Mon, 2023-07-17 at 20:43 -0700, Hugh Dickins wrote:
> > Hi Jeff,
> > 
> > I've been unable to run my kernel builds on ext4 on loop0 on tmpfs
> > swapping load on linux-next recently, on one machine: various kinds
> > of havoc, most common symptoms being ext4_find_dest_de:2107 errors,
> > systemd-journald errors, segfaults.  But no problem observed running
> > on a more recent installation.
> > 
> > Bisected yesterday to 979492850abd ("ext4: convert to ctime accessor
> > functions").
> > 
> > I've mostly averted my eyes from the EXT4_INODE macro changes there,
> > but I think that's where the problem lies.  Reading the comment in
> > fs/ext4/ext4.h above EXT4_FITS_IN_INODE() led me to try "tune2fs -l"
> > and look at /etc/mke2fs.conf.  It's an old installation, its own
> > inodes are 256, but that old mke2fs.conf does default to 128 for small
> > FSes, and what I use for the load test is small.  Passing -I 256 to the
> > mkfs makes the problems go away.
> > 
> > (What's most alarming about the corruption is that it appears to extend
> > beyond just the throwaway test filesystem: segfaults on bash and libc.so
> > from the root filesystem.  But no permanent damage done there.)
> > 
> > One oddity I noticed in scrutinizing that commit, didn't help with
> > the issues above, but there's a hunk in ext4_rename() which changes
> > -	old.dir->i_ctime = old.dir->i_mtime = current_time(old.dir);
> > +	old.dir->i_mtime = inode_set_ctime_current(old.inode);
> > 
> > 
> 
> I suspect the problem here is the i_crtime, which lives wholly in the
> extended part of the inode. The old macros would just not store anything
> if the i_crtime didn't fit, but the new ones would still store the
> tv_sec field in that case, which could be a memory corruptor. This patch
> should fix it, and I'm testing it now.

That makes sense.

> 
> Hugh, if you're able to give this a spin on your setup, then that would
> be most helpful. This is also in the "ctime" branch in my kernel.org
> tree if that helps. If this looks good, I'll ask Christian to fold this
> into the ext4 conversion patch.

Yes, it's now running fine on the problem machine, and on the no-problem.

Tested-by: Hugh Dickins <hughd@xxxxxxxxxx>

> 
> Thanks for the bug report!

And thanks for the quick turnaround!

But I'm puzzled by your dismissing that
-	old.dir->i_ctime = old.dir->i_mtime = current_time(old.dir);
+	old.dir->i_mtime = inode_set_ctime_current(old.inode);
in ext4_rename() as "actually looks fine".

Different issue, nothing to do with the corruption, sure.  Much less
important, sure.  But updating ctime on the wrong inode is "fine"?

Hugh

> 
> ---------------------------8<--------------------------
> 
> [PATCH] ext4: fix the time handling macros when ext4 is using small inodes
> 
> If ext4 is using small on-disk inodes, then it may not be able to store
> fine grained timestamps. It also can't store the i_crtime at all in that
> case since that fully lives in the extended part of the inode.
> 
> 979492850abd got the EXT4_EINODE_{GET,SET}_XTIME macros wrong, and would
> still store the tv_sec field of the i_crtime into the raw_inode, even
> when they were small, corrupting adjacent memory.
> 
> This fixes those macros to skip setting anything in the raw_inode if the
> tv_sec field doesn't fit. 
> 
> Cc: Jan Kara <jack@xxxxxxx>
> Fixes: 979492850abd ("ext4: convert to ctime accessor functions")
> Reported-by: Hugh Dickins <hughd@xxxxxxxxxx>
> Signed-off-by: Jeff Layton <jlayton@xxxxxxxxxx>
> ---
>  fs/ext4/ext4.h | 17 ++++++++++++-----
>  1 file changed, 12 insertions(+), 5 deletions(-)
> 
> diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h
> index 2af347669db7..1e2259d9967d 100644
> --- a/fs/ext4/ext4.h
> +++ b/fs/ext4/ext4.h
> @@ -900,8 +900,10 @@ do {										\
>  #define EXT4_INODE_SET_CTIME(inode, raw_inode)					\
>  	EXT4_INODE_SET_XTIME_VAL(i_ctime, inode, raw_inode, inode_get_ctime(inode))
>  
> -#define EXT4_EINODE_SET_XTIME(xtime, einode, raw_inode)			       \
> -	EXT4_INODE_SET_XTIME_VAL(xtime, &((einode)->vfs_inode), raw_inode, (einode)->xtime)
> +#define EXT4_EINODE_SET_XTIME(xtime, einode, raw_inode)				\
> +	if (EXT4_FITS_IN_INODE(raw_inode, einode, xtime))			\
> +		EXT4_INODE_SET_XTIME_VAL(xtime, &((einode)->vfs_inode),		\
> +					 raw_inode, (einode)->xtime)
>  
>  #define EXT4_INODE_GET_XTIME_VAL(xtime, inode, raw_inode)			\
>  	(EXT4_FITS_IN_INODE(raw_inode, EXT4_I(inode), xtime ## _extra) ?	\
> @@ -922,9 +924,14 @@ do {										\
>  		EXT4_INODE_GET_XTIME_VAL(i_ctime, inode, raw_inode));		\
>  } while (0)
>  
> -#define EXT4_EINODE_GET_XTIME(xtime, einode, raw_inode)			       \
> -do {									       \
> -	(einode)->xtime = EXT4_INODE_GET_XTIME_VAL(xtime, &(einode->vfs_inode), raw_inode);	\
> +#define EXT4_EINODE_GET_XTIME(xtime, einode, raw_inode)				\
> +do {										\
> +	if (EXT4_FITS_IN_INODE(raw_inode, einode, xtime)) 			\
> +		(einode)->xtime =						\
> +			EXT4_INODE_GET_XTIME_VAL(xtime, &(einode->vfs_inode),	\
> +						 raw_inode);			\
> +	else									\
> +		(einode)->xtime = (struct timespec64){0, 0};			\
>  } while (0)
>  
>  #define i_disk_version osd1.linux1.l_i_version
> -- 
> 2.41.0
> 
> 
>