[PATCH RESEND 0/2] Bail out if transaction can cause extent count to overflow

Chandan Babu R
2020-08-01T08:28:29Z

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 2035 [003] 9643.390490: probe:xfs_iflush_int: (ffffffffac6225c0) if_nextents=98511 inode=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 xattr extent counter,
# xfs_db -f -c 'inode 131' -c 'print core.naextents' /dev/loop0
core.naextents = -32561

This patchset adds a new helper function
(i.e. xfs_trans_resv_ext_cnt()) to check for overflow of the per-inode
data and xattr extent counters and invokes it before starting an fs
operation (e.g. creating a new directory entry). With this patchset
applied, XFS detects counter overflows and returns with an error
rather than causing a silent corruption.

The patchset has been tested by executing xfstests with the following
mkfs.xfs options,
1. -m crc=0 -b size=1k
2. -m crc=0 -b size=4k
3. -m crc=0 -b size=512
4. -m rmapbt=1,reflink=1 -b size=1k
5. -m rmapbt=1,reflink=1 -b size=4k

The patches can also be obtained from
https://github.com/chandanr/linux.git at branch xfs-reserve-extent-count-v0.

PS: I am planning to write the code which extends data/xattr extent
counters from 32-bit/16-bit to 64-bit/32-bit on top of these patches.

fs/xfs/libxfs/xfs_attr.c | 33 ++++++++++--
fs/xfs/libxfs/xfs_bmap.c | 7 +++
fs/xfs/libxfs/xfs_trans_resv.c | 33 ++++++++++++
fs/xfs/libxfs/xfs_trans_resv.h | 1 +
fs/xfs/xfs_bmap_item.c | 12 +++++
fs/xfs/xfs_bmap_util.c | 40 ++++++++++++++
fs/xfs/xfs_dquot.c | 7 ++-
fs/xfs/xfs_inode.c | 96 ++++++++++++++++++++++++++++++++++
fs/xfs/xfs_iomap.c | 19 +++++++
fs/xfs/xfs_reflink.c | 35 +++++++++++++
fs/xfs/xfs_rtalloc.c | 4 ++
fs/xfs/xfs_symlink.c | 18 +++++++
12 files changed, 301 insertions(+), 4 deletions(-)

--
2.27.0