Patch "xfs: Honor FALLOC_FL_KEEP_SIZE when punching ends of files" has been added to the 4.9-stable tree

This is a note to let you know that I've just added the patch titled

xfs: Honor FALLOC_FL_KEEP_SIZE when punching ends of files

to the 4.9-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
xfs-honor-falloc_fl_keep_size-when-punching-ends-of-files.patch
and it can be found in the queue-4.9 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Calvin Owens <[email protected]>
Date: Mon, 3 Apr 2017 12:22:29 -0700
Subject: xfs: Honor FALLOC_FL_KEEP_SIZE when punching ends of files

From: Calvin Owens <[email protected]>

commit 3dd09d5a8589c640abb49cfcf92b4ed669eafad1 upstream.

When punching past EOF on XFS, fallocate(mode=PUNCH_HOLE|KEEP_SIZE) will round the file size up to the nearest multiple of PAGE_SIZE:

calvinow@vm-disks/generic-xfs-1 ~$ dd if=/dev/urandom of=test bs=2048 count=1 calvinow@vm-disks/generic-xfs-1 ~$ stat test
Size: 2048 Blocks: 8 IO Block: 4096 regular file
calvinow@vm-disks/generic-xfs-1 ~$ fallocate -n -l 2048 -o 2048 -p test calvinow@vm-disks/generic-xfs-1 ~$ stat test
Size: 4096 Blocks: 8 IO Block: 4096 regular file

Commit 3c2bdc912a1cc050 ("xfs: kill xfs_zero_remaining_bytes") replaced xfs_zero_remaining_bytes() with calls to iomap helpers. The new helpers don't enforce that [pos,offset) lies strictly on [0,i_size) when being called from xfs_free_file_space(), so by "leaking" these ranges into xfs_zero_range() we get this buggy behavior.

Fix this by reintroducing the checks xfs_zero_remaining_bytes() did against i_size at the bottom of xfs_free_file_space().

---
 fs/xfs/xfs_bmap_util.c |   10 +++++++++-
 1 file changed, 9 insertions(+), 1 deletion(-)

@@ -1318,8 +1318,16 @@ xfs_free_file_space(
 	/*
 	 * Now that we've unmap all full blocks we'll have to zero out any
 	 * partial block at the beginning and/or end.  xfs_zero_range is
-	 * smart enough to skip any holes, including those we just created.
+	 * smart enough to skip any holes, including those we just created,
+	 * but we must take care not to zero beyond EOF and enlarge i_size.
 	 */
+
+	if (offset >= XFS_ISIZE(ip))
+		return 0;
+
+	if (offset + len > XFS_ISIZE(ip))
+		len = XFS_ISIZE(ip) - offset;
+
 	return xfs_zero_range(ip, offset, len, NULL);
 }
 

Patches currently in stable-queue which might be from [email protected] are

queue-4.9/xfs-honor-falloc_fl_keep_size-when-punching-ends-of-files.patch