[PATCH 6.18 204/333] iomap: reject delalloc mappings during writeback

Greg Kroah-Hartman
2026-03-17T17:19:44Z

From: Darrick J. Wong <djwong@kernel.org>

commit d320f160aa5ff36cdf83c645cca52b615e866e32 upstream.

Filesystems should never provide a delayed allocation mapping to
writeback; they're supposed to allocate the space before replying.
This can lead to weird IO errors and crashes in the block layer if the
filesystem is being malicious, or if it hadn't set iomap->dev because
it's a delalloc mapping.

Fix this by failing writeback on delalloc mappings. Currently no
filesystems actually misbehave in this manner, but we ought to be
stricter about things like that.

Cc: stable@vger.kernel.org # v5.5
Fixes: 598ecfbaa742ac ("iomap: lift the xfs writeback code to iomap")
Signed-off-by: Darrick J. Wong <djwong@kernel.org>
Link: https://patch.msgid.link/20260302173002.GL13829@frogsfrogsfrogs
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Carlos Maiolino <cmaiolino@redhat.com>
Signed-off-by: Christian Brauner <brauner@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
fs/iomap/ioend.c | 13 +++++++------
1 file changed, 7 insertions(+), 6 deletions(-)

--- a/fs/iomap/ioend.c
+++ b/fs/iomap/ioend.c
@@ -163,17 +163,18 @@ ssize_t iomap_add_to_ioend(struct iomap_
WARN_ON_ONCE(!folio->private && map_len < dirty_len);

switch (wpc->iomap.type) {
- case IOMAP_INLINE:
- WARN_ON_ONCE(1);
- return -EIO;
+ case IOMAP_UNWRITTEN:
+ ioend_flags |= IOMAP_IOEND_UNWRITTEN;
+ break;
+ case IOMAP_MAPPED:
+ break;
case IOMAP_HOLE:
return map_len;
default:
- break;
+ WARN_ON_ONCE(1);
+ return -EIO;
}

- if (wpc->iomap.type == IOMAP_UNWRITTEN)
- ioend_flags |= IOMAP_IOEND_UNWRITTEN;
if (wpc->iomap.flags & IOMAP_F_SHARED)
ioend_flags |= IOMAP_IOEND_SHARED;
if (folio_test_dropbehind(folio))