Re: [PATCH v3] xfs: fix ag count overflow during growfs

[Long Li <leo.lilong@huaweicloud.com>]

Hi, Darrick

I realized there may be a problem with my email so you may not receive my
previous reply. So I'm replying to you with another email address, and if
you received my previous reply, you can ignore this email. Thank you very much!

On Wed, May 24, 2023 at 07:48:00AM -0700, Darrick J. Wong wrote:
> On Wed, May 24, 2023 at 08:10:41PM +0800, Long Li wrote:
> > I found a corruption during growfs:
> > 
> >  XFS (loop0): Internal error agbno >= mp->m_sb.sb_agblocks at line 3661 of
> >    file fs/xfs/libxfs/xfs_alloc.c.  Caller __xfs_free_extent+0x28e/0x3c0
> >  CPU: 0 PID: 573 Comm: xfs_growfs Not tainted 6.3.0-rc7-next-20230420-00001-gda8c95746257
> >  Call Trace:
> >   <TASK>
> >   dump_stack_lvl+0x50/0x70
> >   xfs_corruption_error+0x134/0x150
> >   __xfs_free_extent+0x2c1/0x3c0
> >   xfs_ag_extend_space+0x291/0x3e0
> >   xfs_growfs_data+0xd72/0xe90
> >   xfs_file_ioctl+0x5f9/0x14a0
> >   __x64_sys_ioctl+0x13e/0x1c0
> >   do_syscall_64+0x39/0x80
> >   entry_SYSCALL_64_after_hwframe+0x63/0xcd
> >  XFS (loop0): Corruption detected. Unmount and run xfs_repair
> >  XFS (loop0): Internal error xfs_trans_cancel at line 1097 of file
> >    fs/xfs/xfs_trans.c.  Caller xfs_growfs_data+0x691/0xe90
> >  CPU: 0 PID: 573 Comm: xfs_growfs Not tainted 6.3.0-rc7-next-20230420-00001-gda8c95746257
> >  Call Trace:
> >   <TASK>
> >   dump_stack_lvl+0x50/0x70
> >   xfs_error_report+0x93/0xc0
> >   xfs_trans_cancel+0x2c0/0x350
> >   xfs_growfs_data+0x691/0xe90
> >   xfs_file_ioctl+0x5f9/0x14a0
> >   __x64_sys_ioctl+0x13e/0x1c0
> >   do_syscall_64+0x39/0x80
> >   entry_SYSCALL_64_after_hwframe+0x63/0xcd
> >  RIP: 0033:0x7f2d86706577
> > 
> > The bug can be reproduced with the following sequence:
> > 
> >  # truncate -s  1073741824 xfs_test.img
> >  # mkfs.xfs -f -b size=1024 -d agcount=4 xfs_test.img
> >  # truncate -s 2305843009213693952  xfs_test.img
> >  # mount -o loop xfs_test.img /mnt/test
> >  # xfs_growfs -D  1125899907891200  /mnt/test
> > 
> > The root cause is that during growfs, user space passed in a large value
> > of newblcoks to xfs_growfs_data_private(), due to current sb_agblocks is
> > too small, new AG count will exceed UINT_MAX. Because of AG number type
> > is unsigned int and it would overflow, that caused nagcount much smaller
> > than the actual value. During AG extent space, delta blocks in
> > xfs_resizefs_init_new_ags() will much larger than the actual value due to
> > incorrect nagcount, even exceed UINT_MAX. This will cause corruption and
> > be detected in __xfs_free_extent. Fix it by growing the filesystem to up
> > to the maximally allowed AGs when new AG count overflow.
> > 
> > Signed-off-by: Long Li <leo.lilong@huawei.com>
> > ---
> > v3:
> > - Ensure that the performance is consisent before and after the modification
> >   when nagcount just overflows and 0 < nb_mod < XFS_MIN_AG_BLOCKS. 
> > - Based on Darrick's advice, growing the filesystem to up to the maximally
> >   allowed AGs when new AG count overflow.
> > 
> >  fs/xfs/libxfs/xfs_fs.h |  3 +++
> >  fs/xfs/xfs_fsops.c     | 13 +++++++++----
> >  2 files changed, 12 insertions(+), 4 deletions(-)
> > 
> > diff --git a/fs/xfs/libxfs/xfs_fs.h b/fs/xfs/libxfs/xfs_fs.h
> > index 1cfd5bc6520a..36ec2b1f7e68 100644
> > --- a/fs/xfs/libxfs/xfs_fs.h
> > +++ b/fs/xfs/libxfs/xfs_fs.h
> > @@ -248,6 +248,9 @@ typedef struct xfs_fsop_resblks {
> >  #define XFS_MAX_LOG_BLOCKS	(1024 * 1024ULL)
> >  #define XFS_MIN_LOG_BYTES	(10 * 1024 * 1024ULL)
> >  
> > +/* Maximum number of AGs */
> > +#define XFS_AGNUMBER_MAX	((xfs_agnumber_t)(-1U))
> 
> My apologies, I led you astray.  This should be:
> 
> #define XFS_MAX_AGNUMBER	((xfs_agnumber_t)(NULLAGNUMBER - 1))

OK, it is undoubtedly better to follow the definition in xfsprogs, which will
be modified in the next version.

> 
> since it already exists in multidisk.h from xfsprogs.
> xfs_validate_sb_common probably ought to validate that
> sb_agcount <= XFS_MAX_AGNUMBER as well.

In my understanding the range of sb_agcount should be [1, 0xFFFFFFFF], it
should validate that sb_agcount <= (XFS_MAX_AGNUMBER + 1) , so it's not necessary
to check the upper limit of the sb_agcount.

Thanks,
Long Li

> 
> > +
> >  /*
> >   * Limits on sb_agblocks/sb_agblklog -- mkfs won't format AGs smaller than
> >   * 16MB or larger than 1TB.
> > diff --git a/fs/xfs/xfs_fsops.c b/fs/xfs/xfs_fsops.c
> > index 13851c0d640b..2b37d3e61bdf 100644
> > --- a/fs/xfs/xfs_fsops.c
> > +++ b/fs/xfs/xfs_fsops.c
> > @@ -115,11 +115,16 @@ xfs_growfs_data_private(
> >  
> >  	nb_div = nb;
> >  	nb_mod = do_div(nb_div, mp->m_sb.sb_agblocks);
> > -	nagcount = nb_div + (nb_mod != 0);
> > -	if (nb_mod && nb_mod < XFS_MIN_AG_BLOCKS) {
> > -		nagcount--;
> > -		nb = (xfs_rfsblock_t)nagcount * mp->m_sb.sb_agblocks;
> > +	if (nb_mod && nb_mod >= XFS_MIN_AG_BLOCKS)
> > +		nb_div++;
> > +	else if (nb_mod)
> > +		nb = nb_div * mp->m_sb.sb_agblocks;
> > +
> > +	if (nb_div > XFS_AGNUMBER_MAX) {
> > +		nb_div = XFS_AGNUMBER_MAX;
> > +		nb = nb_div * mp->m_sb.sb_agblocks;
> >  	}
> > +	nagcount = nb_div;
> >  	delta = nb - mp->m_sb.sb_dblocks;
> >  	/*
> >  	 * Reject filesystems with a single AG because they are not
> > -- 
> > 2.31.1
> >