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

Chandan Babu R
2020-10-19T06:41:15Z

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.

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__ */
--
2.28.0