iomap: reject delalloc mappings during writeback

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>

diff --git a/fs/iomap/ioend.c b/fs/iomap/ioend.c
index 4d1ef8a2cee90b91591d387f8e1c3f75350c1da0..60546fa14dfe4d3506c31c18646e7e02ab3804b2 100644 (file)
--- a/fs/iomap/ioend.c
+++ b/fs/iomap/ioend.c
@@ -215,17 +215,18 @@ ssize_t iomap_add_to_ioend(struct iomap_writepage_ctx *wpc, struct folio *folio,
        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))