[PATCH 6.6 0/2] Forbid truncate of fsverity files on btrfs

[PATCH 6.6 0/2] Forbid truncate of fsverity files on btrfs

[Eric Biggers]

Backport the fix to forbid truncate(2) of fsverity files on btrfs (and
also the fix for that fix).

Andrey Albershteyn (1):
  fs,fsverity: remove check for fsverity being enabled in
    setattr_prepare()

Christoph Hellwig (1):
  fs,fsverity: reject size changes on fsverity files in setattr_prepare

 fs/attr.c                | 12 +++++++++++-
 fs/ext4/inode.c          |  4 ----
 fs/f2fs/file.c           |  4 ----
 fs/verity/open.c         |  8 --------
 include/linux/fsverity.h | 25 -------------------------
 5 files changed, 11 insertions(+), 42 deletions(-)


base-commit: a91a6aa9253c64936f0bd8273a2a3c11522ec9c3
-- 
2.56.0

[PATCH 6.6 1/2] fs,fsverity: reject size changes on fsverity files in setattr_prepare

[Eric Biggers]

From: Christoph Hellwig <hch@lst.de>

commit e9734653c523c744f03333ece6ae7a315187f05c upstream.

Add the check to reject truncates of fsverity files directly to
setattr_prepare instead of requiring the file system to handle it.
Besides removing boilerplate code, this also fixes the complete lack of
such check in btrfs.

Fixes: 146054090b08 ("btrfs: initial fsverity support")
Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Jan Kara <jack@suse.cz>
Reviewed-by: "Darrick J. Wong" <djwong@kernel.org>
Link: https://lore.kernel.org/r/20260128152630.627409-2-hch@lst.de
Signed-off-by: Eric Biggers <ebiggers@kernel.org>
---
 fs/attr.c                | 12 +++++++++++-
 fs/ext4/inode.c          |  4 ----
 fs/f2fs/file.c           |  4 ----
 fs/verity/open.c         |  8 --------
 include/linux/fsverity.h | 25 -------------------------
 5 files changed, 11 insertions(+), 42 deletions(-)

diff --git a/fs/attr.c b/fs/attr.c
index a8ae5f6d9b16..c2302fc4b333 100644
--- a/fs/attr.c
+++ b/fs/attr.c
@@ -173,7 +173,17 @@ int setattr_prepare(struct mnt_idmap *idmap, struct dentry *dentry,
 	 * ATTR_FORCE.
 	 */
 	if (ia_valid & ATTR_SIZE) {
-		int error = inode_newsize_ok(inode, attr->ia_size);
+		int error;
+
+		/*
+		 * Verity files are immutable, so deny truncates.  This isn't
+		 * covered by the open-time check because sys_truncate() takes a
+		 * path, not an open file.
+		 */
+		if (IS_ENABLED(CONFIG_FS_VERITY) && IS_VERITY(inode))
+			return -EPERM;
+
+		error = inode_newsize_ok(inode, attr->ia_size);
 		if (error)
 			return error;
 	}
diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
index dea6d27e5028..9ff2958509ed 100644
--- a/fs/ext4/inode.c
+++ b/fs/ext4/inode.c
@@ -5484,10 +5484,6 @@ int ext4_setattr(struct mnt_idmap *idmap, struct dentry *dentry,
 	if (error)
 		return error;
 
-	error = fsverity_prepare_setattr(dentry, attr);
-	if (error)
-		return error;
-
 	if (is_quota_modification(idmap, inode, attr)) {
 		error = dquot_initialize(inode);
 		if (error)
diff --git a/fs/f2fs/file.c b/fs/f2fs/file.c
index 7125117b6322..c1cd6dadabfe 100644
--- a/fs/f2fs/file.c
+++ b/fs/f2fs/file.c
@@ -1065,10 +1065,6 @@ int f2fs_setattr(struct mnt_idmap *idmap, struct dentry *dentry,
 	if (err)
 		return err;
 
-	err = fsverity_prepare_setattr(dentry, attr);
-	if (err)
-		return err;
-
 	if (unlikely(IS_IMMUTABLE(inode)))
 		return -EPERM;
 
diff --git a/fs/verity/open.c b/fs/verity/open.c
index 6c31a871b84b..5342a8e1f781 100644
--- a/fs/verity/open.c
+++ b/fs/verity/open.c
@@ -393,14 +393,6 @@ int __fsverity_file_open(struct inode *inode, struct file *filp)
 }
 EXPORT_SYMBOL_GPL(__fsverity_file_open);
 
-int __fsverity_prepare_setattr(struct dentry *dentry, struct iattr *attr)
-{
-	if (attr->ia_valid & ATTR_SIZE)
-		return -EPERM;
-	return 0;
-}
-EXPORT_SYMBOL_GPL(__fsverity_prepare_setattr);
-
 void __fsverity_cleanup_inode(struct inode *inode)
 {
 	fsverity_free_info(inode->i_verity_info);
diff --git a/include/linux/fsverity.h b/include/linux/fsverity.h
index 1eb7eae580be..139a6f5c6217 100644
--- a/include/linux/fsverity.h
+++ b/include/linux/fsverity.h
@@ -149,7 +149,6 @@ int fsverity_get_digest(struct inode *inode,
 /* open.c */
 
 int __fsverity_file_open(struct inode *inode, struct file *filp);
-int __fsverity_prepare_setattr(struct dentry *dentry, struct iattr *attr);
 void __fsverity_cleanup_inode(struct inode *inode);
 
 /**
@@ -214,12 +213,6 @@ static inline int __fsverity_file_open(struct inode *inode, struct file *filp)
 	return -EOPNOTSUPP;
 }
 
-static inline int __fsverity_prepare_setattr(struct dentry *dentry,
-					     struct iattr *attr)
-{
-	return -EOPNOTSUPP;
-}
-
 static inline void fsverity_cleanup_inode(struct inode *inode)
 {
 }
@@ -301,22 +294,4 @@ static inline int fsverity_file_open(struct inode *inode, struct file *filp)
 	return 0;
 }
 
-/**
- * fsverity_prepare_setattr() - prepare to change a verity inode's attributes
- * @dentry: dentry through which the inode is being changed
- * @attr: attributes to change
- *
- * Verity files are immutable, so deny truncates.  This isn't covered by the
- * open-time check because sys_truncate() takes a path, not a file descriptor.
- *
- * Return: 0 on success, -errno on failure
- */
-static inline int fsverity_prepare_setattr(struct dentry *dentry,
-					   struct iattr *attr)
-{
-	if (IS_VERITY(d_inode(dentry)))
-		return __fsverity_prepare_setattr(dentry, attr);
-	return 0;
-}
-
 #endif	/* _LINUX_FSVERITY_H */
-- 
2.56.0

[PATCH 6.6 2/2] fs,fsverity: remove check for fsverity being enabled in setattr_prepare()

[Eric Biggers]

From: Andrey Albershteyn <aalbersh@kernel.org>

commit d2f96bcb89d36d488a10e3bcf819b98536968286 upstream.

The check that fs-verity is available in the kernel is not necessary
here. Filesystems could have fsverity files even without fs-verity
enabled. In that case, truncate on fsverity file will succeed, what this
check is trying to prevent.

Fixes: e9734653c523 ("fs,fsverity: reject size changes on fsverity files in setattr_prepare")
Cc: stable@vger.kernel.org
Signed-off-by: Andrey Albershteyn <aalbersh@kernel.org>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Link: https://patch.msgid.link/20260727094352.1734826-1-aalbersh@kernel.org
Signed-off-by: Eric Biggers <ebiggers@kernel.org>
---
 fs/attr.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/fs/attr.c b/fs/attr.c
index c2302fc4b333..dd3b0b5115af 100644
--- a/fs/attr.c
+++ b/fs/attr.c
@@ -180,7 +180,7 @@ int setattr_prepare(struct mnt_idmap *idmap, struct dentry *dentry,
 		 * covered by the open-time check because sys_truncate() takes a
 		 * path, not an open file.
 		 */
-		if (IS_ENABLED(CONFIG_FS_VERITY) && IS_VERITY(inode))
+		if (IS_VERITY(inode))
 			return -EPERM;
 
 		error = inode_newsize_ok(inode, attr->ia_size);
-- 
2.56.0

Re: [PATCH 6.6 1/2] fs,fsverity: reject size changes on fsverity files in setattr_prepare

[sashiko-bot]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
- [High] fs: setattr_prepare bypasses fsverity immutability if CONFIG_FS_VERITY=n
--

commit 124beac2c5f385e936a45c9aaf9bc8b5a46a9785
Author: Christoph Hellwig <hch@lst.de>

fs,fsverity: reject size changes on fsverity files in setattr_prepare
    
Add the check to reject truncates of fsverity files directly to
setattr_prepare instead of requiring the file system to handle it.
Besides removing boilerplate code, this also fixes the complete lack of
such check in btrfs.

Link: https://lore.kernel.org/r/20260128152630.627409-2-hch@lst.de

> diff --git a/fs/attr.c b/fs/attr.c
> index a8ae5f6d9b167..c2302fc4b3330 100644
> --- a/fs/attr.c
> +++ b/fs/attr.c
> @@ -173,7 +173,17 @@ int setattr_prepare(struct mnt_idmap *idmap, struct dentry *dentry,
>  	 * ATTR_FORCE.
>  	 */
>  	if (ia_valid & ATTR_SIZE) {
> -		int error = inode_newsize_ok(inode, attr->ia_size);
> +		int error;
> +
> +		/*
> +		 * Verity files are immutable, so deny truncates.  This isn't
> +		 * covered by the open-time check because sys_truncate() takes a
> +		 * path, not an open file.
> +		 */
> +		if (IS_ENABLED(CONFIG_FS_VERITY) && IS_VERITY(inode))
> +			return -EPERM;

[Severity: High]
Is it possible that this IS_ENABLED() guard bypasses the immutability check
when verity is disabled in the kernel?

Ext4 and F2FS previously relied on fsverity_prepare_setattr() which correctly
returned -EOPNOTSUPP on non-verity kernels. By replacing those checks with
this code, if the kernel is compiled without CONFIG_FS_VERITY, this check
evaluates to false and the truncation is allowed to proceed.

Can an unprivileged user with write permissions to a verity file use
sys_truncate() to destroy its contents and cryptographically sealed metadata
on a kernel compiled without CONFIG_FS_VERITY support?

While I noticed this issue is addressed later in the series by commit
0129f7fd3696d1d9b07abe1ecccfcb575dde56d8 ("fs,fsverity: remove check for
fsverity being enabled in setattr_prepare()"), shouldn't this patch be
self-contained and not introduce new regressions?

> +
> +		error = inode_newsize_ok(inode, attr->ia_size);
>  		if (error)
>  			return error;
>  	}

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20261006213815.47194-1-ebiggers@kernel.org?part=1

Re: [PATCH 6.6 0/2] Forbid truncate of fsverity files on btrfs

[Sasha Levin]

> Backport the fix to forbid truncate(2) of fsverity files on btrfs (and
> also the fix for that fix).

Queued the series for 6.6, thanks.

-- 
Thanks,
Sasha