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iomap: reject delalloc mappings during writeback

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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: 598ecfbaa7 ("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>
This commit is contained in:
Darrick J. Wong 2026-03-02 09:30:02 -08:00 • committed by Christian Brauner
parent d3ccc4d86d
commit d320f160aa
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GPG key ID: 91C61BC06578DCA2
1 changed files with 7 additions and 6 deletions
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13
fs/iomap/ioend.c
View file

@ -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))