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

["Darrick J. Wong" <djwong@kernel.org>]

On Tue, Apr 25, 2023 at 10:53:45AM +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 add checks for AG number that
> should not greater than or equal to NULLAGNUMBER before growfs and mount
> filesystem.
> 
> Signed-off-by: Long Li <leo.lilong@huawei.com>
> ---
>  fs/xfs/xfs_fsops.c   | 2 +-
>  fs/xfs/xfs_mount.c   | 6 +++++-
>  fs/xfs/xfs_mount.h   | 2 +-
>  fs/xfs/xfs_rtalloc.c | 2 +-
>  fs/xfs/xfs_super.c   | 4 ++--
>  5 files changed, 10 insertions(+), 6 deletions(-)
> 
> diff --git a/fs/xfs/xfs_fsops.c b/fs/xfs/xfs_fsops.c
> index 13851c0d640b..0f0b12eaf53a 100644
> --- a/fs/xfs/xfs_fsops.c
> +++ b/fs/xfs/xfs_fsops.c
> @@ -100,7 +100,7 @@ xfs_growfs_data_private(
>  	struct xfs_perag	*last_pag;
>  
>  	nb = in->newblocks;
> -	error = xfs_sb_validate_fsb_count(&mp->m_sb, nb);
> +	error = xfs_sb_validate_fsb_count(&mp->m_sb, nb, true);
>  	if (error)
>  		return error;
>  
> diff --git a/fs/xfs/xfs_mount.c b/fs/xfs/xfs_mount.c
> index fb87ffb48f7f..284c11c1c6e8 100644
> --- a/fs/xfs/xfs_mount.c
> +++ b/fs/xfs/xfs_mount.c
> @@ -128,7 +128,8 @@ xfs_uuid_unmount(
>  int
>  xfs_sb_validate_fsb_count(
>  	xfs_sb_t	*sbp,
> -	uint64_t	nblocks)
> +	uint64_t	nblocks,
> +	bool		dblock)
>  {
>  	ASSERT(PAGE_SHIFT >= sbp->sb_blocklog);
>  	ASSERT(sbp->sb_blocklog >= BBSHIFT);
> @@ -136,6 +137,9 @@ xfs_sb_validate_fsb_count(
>  	/* Limited by ULONG_MAX of page cache index */
>  	if (nblocks >> (PAGE_SHIFT - sbp->sb_blocklog) > ULONG_MAX)
>  		return -EFBIG;
> +	/* Limited by NULLAGNUMBER of ag number */
> +	if (dblock && (nblocks >> sbp->sb_agblklog) >= NULLAGNUMBER)
> +		return -EFBIG;

I think this should be a separate predicate to check for overflowing
agcount in xfs_validate_sb_common and xfs_growfs_data_private.

I also wonder if @agcount in xfs_validate_sb_common needs to be u64 (and
not u32) to handle overflows?

Someone should try fuzzing a filesystem with a small agblklog and a
large dblocks to see if one can trip an integer overflow in the
superblock verifier.

--D

>  	return 0;
>  }
>  
> diff --git a/fs/xfs/xfs_mount.h b/fs/xfs/xfs_mount.h
> index f3269c0626f0..a69e9b21ef61 100644
> --- a/fs/xfs/xfs_mount.h
> +++ b/fs/xfs/xfs_mount.h
> @@ -531,7 +531,7 @@ xfs_mod_frextents(struct xfs_mount *mp, int64_t delta)
>  extern int	xfs_readsb(xfs_mount_t *, int);
>  extern void	xfs_freesb(xfs_mount_t *);
>  extern bool	xfs_fs_writable(struct xfs_mount *mp, int level);
> -extern int	xfs_sb_validate_fsb_count(struct xfs_sb *, uint64_t);
> +extern int	xfs_sb_validate_fsb_count(struct xfs_sb *, uint64_t, bool);
>  
>  extern int	xfs_dev_is_read_only(struct xfs_mount *, char *);
>  
> diff --git a/fs/xfs/xfs_rtalloc.c b/fs/xfs/xfs_rtalloc.c
> index 16534e9873f6..c207026d92ac 100644
> --- a/fs/xfs/xfs_rtalloc.c
> +++ b/fs/xfs/xfs_rtalloc.c
> @@ -958,7 +958,7 @@ xfs_growfs_rt(
>  		return -EOPNOTSUPP;
>  
>  	nrblocks = in->newblocks;
> -	error = xfs_sb_validate_fsb_count(sbp, nrblocks);
> +	error = xfs_sb_validate_fsb_count(sbp, nrblocks, false);
>  	if (error)
>  		return error;
>  	/*
> diff --git a/fs/xfs/xfs_super.c b/fs/xfs/xfs_super.c
> index 4d2e87462ac4..72dfd02c588e 100644
> --- a/fs/xfs/xfs_super.c
> +++ b/fs/xfs/xfs_super.c
> @@ -1592,8 +1592,8 @@ xfs_fs_fill_super(
>  	}
>  
>  	/* Ensure this filesystem fits in the page cache limits */
> -	if (xfs_sb_validate_fsb_count(&mp->m_sb, mp->m_sb.sb_dblocks) ||
> -	    xfs_sb_validate_fsb_count(&mp->m_sb, mp->m_sb.sb_rblocks)) {
> +	if (xfs_sb_validate_fsb_count(&mp->m_sb, mp->m_sb.sb_dblocks, true) ||
> +	    xfs_sb_validate_fsb_count(&mp->m_sb, mp->m_sb.sb_rblocks, false)) {
>  		xfs_warn(mp,
>  		"file system too large to be mounted on this system.");
>  		error = -EFBIG;
> -- 
> 2.31.1
>