[PATCH v2 01/31] vfs: pass S_IFDIR mode to vfs_prepare_mode()

[Jori Koolstra]

There is a comment in vfs_prepare_mode() that says:

  Note that it's currently valid for @type to be 0 if a directory is
  created. Filesystems raise that flag individually and we need to check
  whether each filesystem can deal with receiving S_IFDIR from the vfs
  before we enforce a non-zero type.

It is safe to do this clean-up except that three filesystems (fuse,
cifs, and coda) forward the mkdir @mode unchanged to something outside
the kernel. Mask S_IFDIR back out in coda_mkdir(), fuse_mkdir() and
cifs_mkdir() so that what is sent outside the kernel is unchanged.
Their maintainers can drop the mask once they have confirmed it is safe.

Assisted-by: Claude Opus 4.8 (1M context)
Signed-off-by: Jori Koolstra <jkoolstra@xxxxxxxxx>
---
 fs/coda/dir.c         | 7 ++++++-
 fs/fuse/dir.c         | 8 ++++++++
 fs/namei.c            | 7 +------
 fs/smb/client/inode.c | 7 +++++++
 4 files changed, 22 insertions(+), 7 deletions(-)

diff --git a/fs/coda/dir.c b/fs/coda/dir.c
index 835eb7fdfdad..9ad4d217c8b6 100644
--- a/fs/coda/dir.c
+++ b/fs/coda/dir.c
@@ -179,7 +179,12 @@ static struct dentry *coda_mkdir(struct mnt_idmap *idmap, struct inode *dir,
 	if (is_root_inode(dir) && coda_iscontrol(name, len))
 		return ERR_PTR(-EPERM);
 
-	attrs.va_mode = mode;
+	/*
+	 * vfs_mkdir() now passes S_IFDIR in @mode, but @mode is forwarded
+	 * verbatim to userspace, which has only ever been given the permission
+	 * bits. Strip the type bit until venus is known to cope with it.
+	 */
+	attrs.va_mode = mode & ~S_IFDIR;
 	error = venus_mkdir(dir->i_sb, coda_i2f(dir),
 			       name, len, &newfid, &attrs);
 	if (error)
diff --git a/fs/fuse/dir.c b/fs/fuse/dir.c
index 0e2a1039fa43..7decbe4ea48a 100644
--- a/fs/fuse/dir.c
+++ b/fs/fuse/dir.c
@@ -1117,6 +1117,14 @@ static struct dentry *fuse_mkdir(struct mnt_idmap *idmap, struct inode *dir,
 	if (!fm->fc->dont_mask)
 		mode &= ~current_umask();
 
+	/*
+	 * vfs_mkdir() now passes S_IFDIR in @mode, but @mode is forwarded
+	 * verbatim to the userspace server which has only ever been given the
+	 * permission bits. Strip the type bit until the protocol is known to
+	 * cope with it.
+	 */
+	mode &= ~S_IFDIR;
+
 	memset(&inarg, 0, sizeof(inarg));
 	inarg.mode = mode;
 	inarg.umask = current_umask();
diff --git a/fs/namei.c b/fs/namei.c
index 5cc9f0f466b8..6554803d6903 100644
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -4140,11 +4140,6 @@ EXPORT_SYMBOL(end_renaming);
  * after setgid stripping allows the same ordering for both non-POSIX ACL and
  * POSIX ACL supporting filesystems.
  *
- * Note that it's currently valid for @type to be 0 if a directory is created.
- * Filesystems raise that flag individually and we need to check whether each
- * filesystem can deal with receiving S_IFDIR from the vfs before we enforce a
- * non-zero type.
- *
  * Returns: mode to be passed to the filesystem
  */
 static inline umode_t vfs_prepare_mode(struct mnt_idmap *idmap,
@@ -5256,7 +5251,7 @@ struct dentry *vfs_mkdir(struct mnt_idmap *idmap, struct inode *dir,
 	if (!dir->i_op->mkdir)
 		goto err;
 
-	mode = vfs_prepare_mode(idmap, dir, mode, S_IRWXUGO | S_ISVTX, 0);
+	mode = vfs_prepare_mode(idmap, dir, mode, S_IRWXUGO | S_ISVTX, S_IFDIR);
 	error = security_inode_mkdir(dir, dentry, mode);
 	if (error)
 		goto err;
diff --git a/fs/smb/client/inode.c b/fs/smb/client/inode.c
index 1dbcfd163ff0..369dfd56c1e6 100644
--- a/fs/smb/client/inode.c
+++ b/fs/smb/client/inode.c
@@ -2282,6 +2282,13 @@ struct dentry *cifs_mkdir(struct mnt_idmap *idmap, struct inode *inode,
 	const char *full_path;
 	void *page;
 
+	/*
+	 * vfs_mkdir() now passes S_IFDIR in @mode, but @mode is forwarded
+	 * verbatim to the server and in the past only contained permission
+	 * bits. Strip the type bit until SMB is verified to deal with it.
+	 */
+	mode &= ~S_IFDIR;
+
 	cifs_dbg(FYI, "In cifs_mkdir, mode = %04ho inode = 0x%p\n",
 		 mode, inode);
 
-- 
2.54.0