xfs: don't call remap_verify_area with sb write protection held

The XFS_IOC_EXCHANGE_RANGE ioctl with the XFS_EXCHANGE_RANGE_TO_EOF flag
operates on a range bounded by the end of the file.  This means the
actual amount of blocks exchanged is derived from the inode size, which
is only stable with the IOLOCK (i_rwsem) held.  Do that, it currently
calls remap_verify_area from inside the sb write protection which nests
outside the IOLOCK.  But this makes fsnotify_file_area_perm which is
called from remap_verify_area unhappy when the kernel is built with
lockdep and the recently added CONFIG_FANOTIFY_ACCESS_PERMISSIONS
option.

Fix this by always calling remap_verify_area before taking the write
protection, and passing a 0 size to remap_verify_area similar to
the FICLONE/FICLONERANGE ioctls when they are asked to clone until
the file end.

(Note: the size argument gets passed to fsnotify_file_area_perm, but
then isn't actually used there).

Fixes: 9a64d9b ("xfs: introduce new file range exchange ioctl")
Cc: <[email protected]> # v6.10
Signed-off-by: Christoph Hellwig <[email protected]>
Reviewed-by: Darrick J. Wong <[email protected]>
Signed-off-by: Carlos Maiolino <[email protected]>

Author: Christoph Hellwig

fs/xfs/xfs_exchrange.c

@@ -329,22 +329,6 @@ xfs_exchrange_mappings(
  * successfully but before locks are dropped.
  */
 
-/* Verify that we have security clearance to perform this operation. */
-static int
-xfs_exchange_range_verify_area(
-	struct xfs_exchrange	*fxr)
-{
-	int			ret;
-
-	ret = remap_verify_area(fxr->file1, fxr->file1_offset, fxr->length,
-			true);
-	if (ret)
-		return ret;
-
-	return remap_verify_area(fxr->file2, fxr->file2_offset, fxr->length,
-			true);
-}
-
 /*
  * Performs necessary checks before doing a range exchange, having stabilized
  * mutable inode attributes via i_rwsem.
@@ -355,11 +339,13 @@ xfs_exchange_range_checks(
 	unsigned int		alloc_unit)
 {
 	struct inode		*inode1 = file_inode(fxr->file1);
+	loff_t			size1 = i_size_read(inode1);
 	struct inode		*inode2 = file_inode(fxr->file2);
+	loff_t			size2 = i_size_read(inode2);
 	uint64_t		allocmask = alloc_unit - 1;
 	int64_t			test_len;
 	uint64_t		blen;
-	loff_t			size1, size2, tmp;
+	loff_t			tmp;
 	int			error;
 
 	/* Don't touch certain kinds of inodes */
@@ -368,24 +354,25 @@ xfs_exchange_range_checks(
 	if (IS_SWAPFILE(inode1) || IS_SWAPFILE(inode2))
 		return -ETXTBSY;
 
-	size1 = i_size_read(inode1);
-	size2 = i_size_read(inode2);
-
 	/* Ranges cannot start after EOF. */
 	if (fxr->file1_offset > size1 || fxr->file2_offset > size2)
 		return -EINVAL;
 
-	/*
-	 * If the caller said to exchange to EOF, we set the length of the
-	 * request large enough to cover everything to the end of both files.
-	 */
 	if (fxr->flags & XFS_EXCHANGE_RANGE_TO_EOF) {
+		/*
+		 * If the caller said to exchange to EOF, we set the length of
+		 * the request large enough to cover everything to the end of
+		 * both files.
+		 */
 		fxr->length = max_t(int64_t, size1 - fxr->file1_offset,
 					     size2 - fxr->file2_offset);
-
-		error = xfs_exchange_range_verify_area(fxr);
-		if (error)
-			return error;
+	} else {
+		/*
+		 * Otherwise we require both ranges to end within EOF.
+		 */
+		if (fxr->file1_offset + fxr->length > size1 ||
+		    fxr->file2_offset + fxr->length > size2)
+			return -EINVAL;
 	}
 
 	/*
@@ -401,15 +388,6 @@ xfs_exchange_range_checks(
 	    check_add_overflow(fxr->file2_offset, fxr->length, &tmp))
 		return -EINVAL;
 
-	/*
-	 * We require both ranges to end within EOF, unless we're exchanging
-	 * to EOF.
-	 */
-	if (!(fxr->flags & XFS_EXCHANGE_RANGE_TO_EOF) &&
-	    (fxr->file1_offset + fxr->length > size1 ||
-	     fxr->file2_offset + fxr->length > size2))
-		return -EINVAL;
-
 	/*
 	 * Make sure we don't hit any file size limits.  If we hit any size
 	 * limits such that test_length was adjusted, we abort the whole
@@ -747,6 +725,7 @@ xfs_exchange_range(
 {
 	struct inode		*inode1 = file_inode(fxr->file1);
 	struct inode		*inode2 = file_inode(fxr->file2);
+	loff_t			check_len = fxr->length;
 	int			ret;
 
 	BUILD_BUG_ON(XFS_EXCHANGE_RANGE_ALL_FLAGS &
@@ -779,14 +758,18 @@ xfs_exchange_range(
 		return -EBADF;
 
 	/*
-	 * If we're not exchanging to EOF, we can check the areas before
-	 * stabilizing both files' i_size.
+	 * If we're exchanging to EOF we can't calculate the length until taking
+	 * the iolock.  Pass a 0 length to remap_verify_area similar to the
+	 * FICLONE and FICLONERANGE ioctls that support cloning to EOF as well.
 	 */
-	if (!(fxr->flags & XFS_EXCHANGE_RANGE_TO_EOF)) {
-		ret = xfs_exchange_range_verify_area(fxr);
-		if (ret)
-			return ret;
-	}
+	if (fxr->flags & XFS_EXCHANGE_RANGE_TO_EOF)
+		check_len = 0;
+	ret = remap_verify_area(fxr->file1, fxr->file1_offset, check_len, true);
+	if (ret)
+		return ret;
+	ret = remap_verify_area(fxr->file2, fxr->file2_offset, check_len, true);
+	if (ret)
+		return ret;
 
 	/* Update cmtime if the fd/inode don't forbid it. */
 	if (!(fxr->file1->f_mode & FMODE_NOCMTIME) && !IS_NOCMTIME(inode1))