[PATCH 1/2] open: new O_REGULAR flag support

[Dorjoy Chowdhury <dorjoychy111@gmail.com>]

This flag indicates the path should be opened if it's a regular file.
A relevant error code ENOTREGULAR(35) has been introduced. For example,
if open is called on path /dev/null with O_REGULAR in the flag param,
it will return -ENOTREGULAR.

When used in combination with O_CREAT, either the regular file is
created, or if the path already exists, it is opened if it's a regular
file. Otherwise, -ENOTREGULAR is returned.

-EINVAL is returned when O_REGULAR is combined with O_DIRECTORY (not
part of O_TMPFILE) because it doesn't make sense to open a path that
is both a directory and a regular file.

Signed-off-by: Dorjoy Chowdhury <dorjoychy111@gmail.com>
---
 fs/fcntl.c                            | 2 +-
 fs/namei.c                            | 6 ++++++
 fs/open.c                             | 4 +++-
 include/linux/fcntl.h                 | 2 +-
 include/uapi/asm-generic/errno-base.h | 1 +
 include/uapi/asm-generic/fcntl.h      | 4 ++++
 6 files changed, 16 insertions(+), 3 deletions(-)

diff --git a/fs/fcntl.c b/fs/fcntl.c
index f93dbca08435..62ab4ad2b6f5 100644
--- a/fs/fcntl.c
+++ b/fs/fcntl.c
@@ -1169,7 +1169,7 @@ static int __init fcntl_init(void)
 	 * Exceptions: O_NONBLOCK is a two bit define on parisc; O_NDELAY
 	 * is defined as O_NONBLOCK on some platforms and not on others.
 	 */
-	BUILD_BUG_ON(20 - 1 /* for O_RDONLY being 0 */ !=
+	BUILD_BUG_ON(21 - 1 /* for O_RDONLY being 0 */ !=
 		HWEIGHT32(
 			(VALID_OPEN_FLAGS & ~(O_NONBLOCK | O_NDELAY)) |
 			__FMODE_EXEC));
diff --git a/fs/namei.c b/fs/namei.c
index cf16b6822dd3..365f3cc77e1c 100644
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -4617,6 +4617,10 @@ static int do_open(struct nameidata *nd,
 		if (unlikely(error))
 			return error;
 	}
+
+	if ((open_flag & O_REGULAR) && !d_is_reg(nd->path.dentry))
+		return -ENOTREGULAR;
+
 	if ((nd->flags & LOOKUP_DIRECTORY) && !d_can_lookup(nd->path.dentry))
 		return -ENOTDIR;
 
@@ -4766,6 +4770,8 @@ static int do_o_path(struct nameidata *nd, unsigned flags, struct file *file)
 	struct path path;
 	int error = path_lookupat(nd, flags, &path);
 	if (!error) {
+		if ((file->f_flags & O_REGULAR) && !d_is_reg(path.dentry))
+			return -ENOTREGULAR;
 		audit_inode(nd->name, path.dentry, 0);
 		error = vfs_open(&path, file);
 		path_put(&path);
diff --git a/fs/open.c b/fs/open.c
index f328622061c5..670cd6b4967a 100644
--- a/fs/open.c
+++ b/fs/open.c
@@ -1212,7 +1212,7 @@ struct file *kernel_file_open(const struct path *path, int flags,
 EXPORT_SYMBOL_GPL(kernel_file_open);
 
 #define WILL_CREATE(flags)	(flags & (O_CREAT | __O_TMPFILE))
-#define O_PATH_FLAGS		(O_DIRECTORY | O_NOFOLLOW | O_PATH | O_CLOEXEC)
+#define O_PATH_FLAGS		(O_DIRECTORY | O_NOFOLLOW | O_PATH | O_CLOEXEC | O_REGULAR)
 
 inline struct open_how build_open_how(int flags, umode_t mode)
 {
@@ -1289,6 +1289,8 @@ inline int build_open_flags(const struct open_how *how, struct open_flags *op)
 			return -EINVAL;
 		if (!(acc_mode & MAY_WRITE))
 			return -EINVAL;
+	} else if ((flags & O_DIRECTORY) && (flags & O_REGULAR)) {
+		return -EINVAL;
 	}
 	if (flags & O_PATH) {
 		/* O_PATH only permits certain other flags to be set. */
diff --git a/include/linux/fcntl.h b/include/linux/fcntl.h
index a332e79b3207..4fd07b0e0a17 100644
--- a/include/linux/fcntl.h
+++ b/include/linux/fcntl.h
@@ -10,7 +10,7 @@
 	(O_RDONLY | O_WRONLY | O_RDWR | O_CREAT | O_EXCL | O_NOCTTY | O_TRUNC | \
 	 O_APPEND | O_NDELAY | O_NONBLOCK | __O_SYNC | O_DSYNC | \
 	 FASYNC	| O_DIRECT | O_LARGEFILE | O_DIRECTORY | O_NOFOLLOW | \
-	 O_NOATIME | O_CLOEXEC | O_PATH | __O_TMPFILE)
+	 O_NOATIME | O_CLOEXEC | O_PATH | __O_TMPFILE | O_REGULAR)
 
 /* List of all valid flags for the how->resolve argument: */
 #define VALID_RESOLVE_FLAGS \
diff --git a/include/uapi/asm-generic/errno-base.h b/include/uapi/asm-generic/errno-base.h
index 9653140bff92..ea9a96d30737 100644
--- a/include/uapi/asm-generic/errno-base.h
+++ b/include/uapi/asm-generic/errno-base.h
@@ -36,5 +36,6 @@
 #define	EPIPE		32	/* Broken pipe */
 #define	EDOM		33	/* Math argument out of domain of func */
 #define	ERANGE		34	/* Math result not representable */
+#define	ENOTREGULAR	35      /* Not a regular file */
 
 #endif
diff --git a/include/uapi/asm-generic/fcntl.h b/include/uapi/asm-generic/fcntl.h
index 613475285643..11e5eadab868 100644
--- a/include/uapi/asm-generic/fcntl.h
+++ b/include/uapi/asm-generic/fcntl.h
@@ -88,6 +88,10 @@
 #define __O_TMPFILE	020000000
 #endif
 
+#ifndef O_REGULAR
+#define O_REGULAR       040000000
+#endif
+
 /* a horrid kludge trying to make sure that this will fail on old kernels */
 #define O_TMPFILE (__O_TMPFILE | O_DIRECTORY)
 
-- 
2.52.0