Re: [PATCH V7 01/14] xfs: Add helper for checking per-inode extent count overflow

Allison Henderson
2020-10-24T19:30:47Z

On 10/18/20 11:40 PM, Chandan Babu R wrote:
> XFS does not check for possible overflow of per-inode extent counter
> fields when adding extents to either data or attr fork.
>
> For e.g.
> 1. Insert 5 million xattrs (each having a value size of 255 bytes) and
> then delete 50% of them in an alternating manner.
>
> 2. On a 4k block sized XFS filesystem instance, the above causes 98511
> extents to be created in the attr fork of the inode.
>
> xfsaild/loop0 2008 [003] 1475.127209: probe:xfs_inode_to_disk: (ffffffffa43fb6b0) if_nextents=98511 i_ino=131
>
> 3. The incore inode fork extent counter is a signed 32-bit
> quantity. However the on-disk extent counter is an unsigned 16-bit
> quantity and hence cannot hold 98511 extents.
>
> 4. The following incorrect value is stored in the attr extent counter,
> # xfs_db -f -c 'inode 131' -c 'print core.naextents' /dev/loop0
> core.naextents = -32561
>
> This commit adds a new helper function (i.e.
> xfs_iext_count_may_overflow()) to check for overflow of the per-inode
> data and xattr extent counters. Future patches will use this function to
> make sure that an FS operation won't cause the extent counter to
> overflow.
>
Looks good to me
Reviewed-by: Allison Henderson <allison.henderson@oracle.com>

> Suggested-by: Darrick J. Wong <darrick.wong@oracle.com>
> Reviewed-by: Christoph Hellwig <hch@lst.de>
> Reviewed-by: Darrick J. Wong <darrick.wong@oracle.com>
> Signed-off-by: Chandan Babu R <chandanrlinux@gmail.com>
> ---
> fs/xfs/libxfs/xfs_inode_fork.c | 23 +++++++++++++++++++++++
> fs/xfs/libxfs/xfs_inode_fork.h | 2 ++
> 2 files changed, 25 insertions(+)
>
> diff --git a/fs/xfs/libxfs/xfs_inode_fork.c b/fs/xfs/libxfs/xfs_inode_fork.c
> index 7575de5cecb1..8d48716547e5 100644
> --- a/fs/xfs/libxfs/xfs_inode_fork.c
> +++ b/fs/xfs/libxfs/xfs_inode_fork.c
> @@ -23,6 +23,7 @@
> #include "xfs_da_btree.h"
> #include "xfs_dir2_priv.h"
> #include "xfs_attr_leaf.h"
> +#include "xfs_types.h"
>
> kmem_zone_t *xfs_ifork_zone;
>
> @@ -728,3 +729,25 @@ xfs_ifork_verify_local_attr(
>
> return 0;
> }
> +
> +int
> +xfs_iext_count_may_overflow(
> + struct xfs_inode *ip,
> + int whichfork,
> + int nr_to_add)
> +{
> + struct xfs_ifork *ifp = XFS_IFORK_PTR(ip, whichfork);
> + uint64_t max_exts;
> + uint64_t nr_exts;
> +
> + if (whichfork == XFS_COW_FORK)
> + return 0;
> +
> + max_exts = (whichfork == XFS_ATTR_FORK) ? MAXAEXTNUM : MAXEXTNUM;
> +
> + nr_exts = ifp->if_nextents + nr_to_add;
> + if (nr_exts < ifp->if_nextents || nr_exts > max_exts)
> + return -EFBIG;
> +
> + return 0;
> +}
> diff --git a/fs/xfs/libxfs/xfs_inode_fork.h b/fs/xfs/libxfs/xfs_inode_fork.h
> index a4953e95c4f3..0beb8e2a00be 100644
> --- a/fs/xfs/libxfs/xfs_inode_fork.h
> +++ b/fs/xfs/libxfs/xfs_inode_fork.h
> @@ -172,5 +172,7 @@ extern void xfs_ifork_init_cow(struct xfs_inode *ip);
>
> int xfs_ifork_verify_local_data(struct xfs_inode *ip);
> int xfs_ifork_verify_local_attr(struct xfs_inode *ip);
> +int xfs_iext_count_may_overflow(struct xfs_inode *ip, int whichfork,
> + int nr_to_add);
>
> #endif /* __XFS_INODE_FORK_H__ */
>