[PATCH v2] iomap: reject delalloc mappings during writeback

[PATCH v2] iomap: reject delalloc mappings during writeback

[Darrick J. Wong]

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

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>
---
v2: futureproof new iomap types
---
 fs/iomap/ioend.c |   13 +++++++------
 1 file changed, 7 insertions(+), 6 deletions(-)

diff --git a/fs/iomap/ioend.c b/fs/iomap/ioend.c
index 4d1ef8a2cee90b..60546fa14dfe4d 100644
--- 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))

Re: [PATCH v2] iomap: reject delalloc mappings during writeback

[Christoph Hellwig]

Looks good:

Reviewed-by: Christoph Hellwig <hch@lst.de>

Re: [PATCH v2] iomap: reject delalloc mappings during writeback

[Carlos Maiolino]

On Thu, Feb 26, 2026 at 03:34:42PM -0800, Darrick J. Wong wrote:
> From: Darrick J. Wong <djwong@kernel.org>
> 
> 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.

Looks good.
Reviewed-by: Carlos Maiolino <cmaiolino@redhat.com>

> 
> 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>
> ---
> v2: futureproof new iomap types
> ---
>  fs/iomap/ioend.c |   13 +++++++------
>  1 file changed, 7 insertions(+), 6 deletions(-)
> 
> diff --git a/fs/iomap/ioend.c b/fs/iomap/ioend.c
> index 4d1ef8a2cee90b..60546fa14dfe4d 100644
> --- 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))
> 

[PATCH v3] iomap: reject delalloc mappings during writeback

[Darrick J. Wong]

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

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>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Carlos Maiolino <cmaiolino@redhat.com>
---
v3: add review tags
v2: futureproof new iomap types
---
 fs/iomap/ioend.c |   13 +++++++------
 1 file changed, 7 insertions(+), 6 deletions(-)

diff --git a/fs/iomap/ioend.c b/fs/iomap/ioend.c
index 4d1ef8a2cee90b..60546fa14dfe4d 100644
--- 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))

Re: [PATCH v3] iomap: reject delalloc mappings during writeback

[Christian Brauner]

On Mon, 02 Mar 2026 09:30:02 -0800, Darrick J. Wong wrote:
> 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.
> 
> [...]

Applied to the vfs.fixes branch of the vfs/vfs.git tree.
Patches in the vfs.fixes branch should appear in linux-next soon.

Please report any outstanding bugs that were missed during review in a
new review to the original patch series allowing us to drop it.

It's encouraged to provide Acked-bys and Reviewed-bys even though the
patch has now been applied. If possible patch trailers will be updated.

Note that commit hashes shown below are subject to change due to rebase,
trailer updates or similar. If in doubt, please check the listed branch.

tree:   https://git.kernel.org/pub/scm/linux/kernel/git/vfs/vfs.git
branch: vfs.fixes

[1/1] iomap: reject delalloc mappings during writeback
      https://git.kernel.org/vfs/vfs/c/d320f160aa5f