From: Chandan Babu R <redacted>

Source kernel commit: b9b7e1dc56c5ca8d6fc37c410b054e9f26737d2e

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,
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 <redacted>
Reviewed-by: Allison Henderson <redacted>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Darrick J. Wong <redacted>
Signed-off-by: Chandan Babu R <redacted>
Signed-off-by: Darrick J. Wong <redacted>
Signed-off-by: Allison Henderson <redacted>
---
 libxfs/xfs_inode_fork.c | 23 +++++++++++++++++++++++
 libxfs/xfs_inode_fork.h |  2 ++
 2 files changed, 25 insertions(+)

diff --git a/libxfs/xfs_inode_fork.c b/libxfs/xfs_inode_fork.c
index 0b1af501..83866cd 100644
--- a/libxfs/xfs_inode_fork.c
+++ b/libxfs/xfs_inode_fork.c

@@ -21,6 +21,7 @@
 #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;
 

@@ -726,3 +727,25 @@ 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/libxfs/xfs_inode_fork.h b/libxfs/xfs_inode_fork.h
index a4953e9..0beb8e2 100644
--- a/libxfs/xfs_inode_fork.h
+++ b/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__ */

-- 
2.7.4