This flag indicates the path should be opened if it's a regular file.
This is useful to write secure programs that want to avoid being tricked
into opening device nodes with special semantics while thinking they
operate on regular files.

A corresponding error code ENOTREG has been introduced. For example, if
open is called on path /dev/null with O_REGULAR in the flag param, it
will return -ENOTREG.

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, -ENOTREG 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>
---
 arch/alpha/include/uapi/asm/errno.h        | 2 ++
 arch/alpha/include/uapi/asm/fcntl.h        | 1 +
 arch/mips/include/uapi/asm/errno.h         | 2 ++
 arch/parisc/include/uapi/asm/errno.h       | 2 ++
 arch/parisc/include/uapi/asm/fcntl.h       | 1 +
 arch/sparc/include/uapi/asm/errno.h        | 2 ++
 arch/sparc/include/uapi/asm/fcntl.h        | 1 +
 fs/fcntl.c                                 | 2 +-
 fs/namei.c                                 | 6 ++++++
 fs/open.c                                  | 4 +++-
 include/linux/fcntl.h                      | 2 +-
 include/uapi/asm-generic/errno.h           | 2 ++
 include/uapi/asm-generic/fcntl.h           | 4 ++++
 tools/arch/alpha/include/uapi/asm/errno.h  | 2 ++
 tools/arch/mips/include/uapi/asm/errno.h   | 2 ++
 tools/arch/parisc/include/uapi/asm/errno.h | 2 ++
 tools/arch/sparc/include/uapi/asm/errno.h  | 2 ++
 tools/include/uapi/asm-generic/errno.h     | 2 ++
 18 files changed, 38 insertions(+), 3 deletions(-)

diff --git a/arch/alpha/include/uapi/asm/errno.h b/arch/alpha/include/uapi/asm/errno.h
index 6791f6508632..8bbcaa9024f9 100644
--- a/arch/alpha/include/uapi/asm/errno.h
+++ b/arch/alpha/include/uapi/asm/errno.h
@@ -127,4 +127,6 @@
 
 #define EHWPOISON	139	/* Memory page has hardware error */
 
+#define ENOTREG		140	/* Not a regular file */
+
 #endif
diff --git a/arch/alpha/include/uapi/asm/fcntl.h b/arch/alpha/include/uapi/asm/fcntl.h
index 50bdc8e8a271..4da5a64c23bd 100644
--- a/arch/alpha/include/uapi/asm/fcntl.h
+++ b/arch/alpha/include/uapi/asm/fcntl.h
@@ -34,6 +34,7 @@
 
 #define O_PATH		040000000
 #define __O_TMPFILE	0100000000
+#define O_REGULAR	0200000000
 
 #define F_GETLK		7
 #define F_SETLK		8
diff --git a/arch/mips/include/uapi/asm/errno.h b/arch/mips/include/uapi/asm/errno.h
index c01ed91b1ef4..293c78777254 100644
--- a/arch/mips/include/uapi/asm/errno.h
+++ b/arch/mips/include/uapi/asm/errno.h
@@ -126,6 +126,8 @@
 
 #define EHWPOISON	168	/* Memory page has hardware error */
 
+#define ENOTREG		169	/* Not a regular file */
+
 #define EDQUOT		1133	/* Quota exceeded */
 
 
diff --git a/arch/parisc/include/uapi/asm/errno.h b/arch/parisc/include/uapi/asm/errno.h
index 8cbc07c1903e..442917484f99 100644
--- a/arch/parisc/include/uapi/asm/errno.h
+++ b/arch/parisc/include/uapi/asm/errno.h
@@ -124,4 +124,6 @@
 
 #define EHWPOISON	257	/* Memory page has hardware error */
 
+#define ENOTREG		258	/* Not a regular file */
+
 #endif
diff --git a/arch/parisc/include/uapi/asm/fcntl.h b/arch/parisc/include/uapi/asm/fcntl.h
index 03dee816cb13..0cc3320fe326 100644
--- a/arch/parisc/include/uapi/asm/fcntl.h
+++ b/arch/parisc/include/uapi/asm/fcntl.h
@@ -19,6 +19,7 @@
 
 #define O_PATH		020000000
 #define __O_TMPFILE	040000000
+#define O_REGULAR	0100000000
 
 #define F_GETLK64	8
 #define F_SETLK64	9
diff --git a/arch/sparc/include/uapi/asm/errno.h b/arch/sparc/include/uapi/asm/errno.h
index 4a41e7835fd5..8dce0bfeab74 100644
--- a/arch/sparc/include/uapi/asm/errno.h
+++ b/arch/sparc/include/uapi/asm/errno.h
@@ -117,4 +117,6 @@
 
 #define EHWPOISON	135	/* Memory page has hardware error */
 
+#define ENOTREG		136	/* Not a regular file */
+
 #endif
diff --git a/arch/sparc/include/uapi/asm/fcntl.h b/arch/sparc/include/uapi/asm/fcntl.h
index 67dae75e5274..a93d18d2c23e 100644
--- a/arch/sparc/include/uapi/asm/fcntl.h
+++ b/arch/sparc/include/uapi/asm/fcntl.h
@@ -37,6 +37,7 @@
 
 #define O_PATH		0x1000000
 #define __O_TMPFILE	0x2000000
+#define O_REGULAR	0x4000000
 
 #define F_GETOWN	5	/*  for sockets. */
 #define F_SETOWN	6	/*  for sockets. */
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 b28ecb699f32..f5504ae4b03c 100644
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -4616,6 +4616,10 @@ static int do_open(struct nameidata *nd,
 		if (unlikely(error))
 			return error;
 	}
+
+	if ((open_flag & O_REGULAR) && !d_is_reg(nd->path.dentry))
+		return -ENOTREG;
+
 	if ((nd->flags & LOOKUP_DIRECTORY) && !d_can_lookup(nd->path.dentry))
 		return -ENOTDIR;
 
@@ -4765,6 +4769,8 @@ 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 -ENOTREG;
 		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 74c4c1462b3e..82153e21907e 100644
--- a/fs/open.c
+++ b/fs/open.c
@@ -1173,7 +1173,7 @@ 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)
 {
@@ -1250,6 +1250,8 @@ 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.h b/include/uapi/asm-generic/errno.h
index 92e7ae493ee3..2216ab9aa32e 100644
--- a/include/uapi/asm-generic/errno.h
+++ b/include/uapi/asm-generic/errno.h
@@ -122,4 +122,6 @@
 
 #define EHWPOISON	133	/* Memory page has hardware error */
 
+#define ENOTREG		134	/* Not a regular file */
+
 #endif
diff --git a/include/uapi/asm-generic/fcntl.h b/include/uapi/asm-generic/fcntl.h
index 613475285643..3468b352a575 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)
 
diff --git a/tools/arch/alpha/include/uapi/asm/errno.h b/tools/arch/alpha/include/uapi/asm/errno.h
index 6791f6508632..8bbcaa9024f9 100644
--- a/tools/arch/alpha/include/uapi/asm/errno.h
+++ b/tools/arch/alpha/include/uapi/asm/errno.h
@@ -127,4 +127,6 @@
 
 #define EHWPOISON	139	/* Memory page has hardware error */
 
+#define ENOTREG		140	/* Not a regular file */
+
 #endif
diff --git a/tools/arch/mips/include/uapi/asm/errno.h b/tools/arch/mips/include/uapi/asm/errno.h
index c01ed91b1ef4..293c78777254 100644
--- a/tools/arch/mips/include/uapi/asm/errno.h
+++ b/tools/arch/mips/include/uapi/asm/errno.h
@@ -126,6 +126,8 @@
 
 #define EHWPOISON	168	/* Memory page has hardware error */
 
+#define ENOTREG		169	/* Not a regular file */
+
 #define EDQUOT		1133	/* Quota exceeded */
 
 
diff --git a/tools/arch/parisc/include/uapi/asm/errno.h b/tools/arch/parisc/include/uapi/asm/errno.h
index 8cbc07c1903e..442917484f99 100644
--- a/tools/arch/parisc/include/uapi/asm/errno.h
+++ b/tools/arch/parisc/include/uapi/asm/errno.h
@@ -124,4 +124,6 @@
 
 #define EHWPOISON	257	/* Memory page has hardware error */
 
+#define ENOTREG		258	/* Not a regular file */
+
 #endif
diff --git a/tools/arch/sparc/include/uapi/asm/errno.h b/tools/arch/sparc/include/uapi/asm/errno.h
index 4a41e7835fd5..8dce0bfeab74 100644
--- a/tools/arch/sparc/include/uapi/asm/errno.h
+++ b/tools/arch/sparc/include/uapi/asm/errno.h
@@ -117,4 +117,6 @@
 
 #define EHWPOISON	135	/* Memory page has hardware error */
 
+#define ENOTREG		136	/* Not a regular file */
+
 #endif
diff --git a/tools/include/uapi/asm-generic/errno.h b/tools/include/uapi/asm-generic/errno.h
index 92e7ae493ee3..2216ab9aa32e 100644
--- a/tools/include/uapi/asm-generic/errno.h
+++ b/tools/include/uapi/asm-generic/errno.h
@@ -122,4 +122,6 @@
 
 #define EHWPOISON	133	/* Memory page has hardware error */
 
+#define ENOTREG		134	/* Not a regular file */
+
 #endif
-- 
2.52.0

Just a happy path test.

Signed-off-by: Dorjoy Chowdhury <dorjoychy111@gmail.com>
---
 .../testing/selftests/openat2/openat2_test.c  | 37 ++++++++++++++++++-
 1 file changed, 36 insertions(+), 1 deletion(-)

diff --git a/tools/testing/selftests/openat2/openat2_test.c b/tools/testing/selftests/openat2/openat2_test.c
index 0e161ef9e9e4..011ebc9af4e5 100644
--- a/tools/testing/selftests/openat2/openat2_test.c
+++ b/tools/testing/selftests/openat2/openat2_test.c
@@ -320,8 +320,42 @@ void test_openat2_flags(void)
 	}
 }
 
+#ifndef O_REGULAR
+#define O_REGULAR 040000000
+#endif
+
+#ifndef ENOTREG
+#define ENOTREG 134
+#endif
+
+void test_openat2_o_regular_flag(void)
+{
+	if (!openat2_supported) {
+		ksft_test_result_skip("Skipping %s as openat2 is not supported\n", __func__);
+		return;
+	}
+
+	struct open_how how = {
+		.flags = O_REGULAR | O_RDONLY
+	};
+
+	int fd = sys_openat2(AT_FDCWD, "/dev/null", &how);
+
+	if (fd == ENOENT) {
+		ksft_test_result_skip("Skipping %s as there is no /dev/null\n", __func__);
+		return;
+	}
+
+	if (fd != -ENOTREG) {
+		ksft_test_result_fail("openat2 should return ENOTREG\n");
+		return;
+	}
+
+	ksft_test_result_pass("%s succeeded\n", __func__);
+}
+
 #define NUM_TESTS (NUM_OPENAT2_STRUCT_VARIATIONS * NUM_OPENAT2_STRUCT_TESTS + \
-		   NUM_OPENAT2_FLAG_TESTS)
+		   NUM_OPENAT2_FLAG_TESTS + 1)
 
 int main(int argc, char **argv)
 {
@@ -330,6 +364,7 @@ int main(int argc, char **argv)
 
 	test_openat2_struct();
 	test_openat2_flags();
+	test_openat2_o_regular_flag();
 
 	if (ksft_get_fail_cnt() + ksft_get_error_cnt() > 0)
 		ksft_exit_fail();
-- 
2.52.0

Following the convention in include/uapi/asm-generic/fcntl.h and other
architecture specific arch/*/include/uapi/asm/fcntl.h files.

Signed-off-by: Dorjoy Chowdhury <dorjoychy111@gmail.com>
---
 arch/sparc/include/uapi/asm/fcntl.h | 36 ++++++++++++++---------------
 1 file changed, 18 insertions(+), 18 deletions(-)

diff --git a/arch/sparc/include/uapi/asm/fcntl.h b/arch/sparc/include/uapi/asm/fcntl.h
index a93d18d2c23e..3c16f1a66a6a 100644
--- a/arch/sparc/include/uapi/asm/fcntl.h
+++ b/arch/sparc/include/uapi/asm/fcntl.h
@@ -2,23 +2,23 @@
 #ifndef _SPARC_FCNTL_H
 #define _SPARC_FCNTL_H
 
-#define O_APPEND	0x0008
-#define FASYNC		0x0040	/* fcntl, for BSD compatibility */
-#define O_CREAT		0x0200	/* not fcntl */
-#define O_TRUNC		0x0400	/* not fcntl */
-#define O_EXCL		0x0800	/* not fcntl */
-#define O_DSYNC		0x2000	/* used to be O_SYNC, see below */
-#define O_NONBLOCK	0x4000
+#define O_APPEND	0000000010
+#define FASYNC		0000000100	/* fcntl, for BSD compatibility */
+#define O_CREAT		0000001000	/* not fcntl */
+#define O_TRUNC		0000002000	/* not fcntl */
+#define O_EXCL		0000004000	/* not fcntl */
+#define O_DSYNC		0000020000	/* used to be O_SYNC, see below */
+#define O_NONBLOCK	0000040000
 #if defined(__sparc__) && defined(__arch64__)
-#define O_NDELAY	0x0004
+#define O_NDELAY	0000000004
 #else
-#define O_NDELAY	(0x0004 | O_NONBLOCK)
+#define O_NDELAY	(0000000004 | O_NONBLOCK)
 #endif
-#define O_NOCTTY	0x8000	/* not fcntl */
-#define O_LARGEFILE	0x40000
-#define O_DIRECT        0x100000 /* direct disk access hint */
-#define O_NOATIME	0x200000
-#define O_CLOEXEC	0x400000
+#define O_NOCTTY	0000100000	/* not fcntl */
+#define O_LARGEFILE	0001000000
+#define O_DIRECT        0004000000 /* direct disk access hint */
+#define O_NOATIME	0010000000
+#define O_CLOEXEC	0020000000
 /*
  * Before Linux 2.6.33 only O_DSYNC semantics were implemented, but using
  * the O_SYNC flag.  We continue to use the existing numerical value
@@ -32,12 +32,12 @@
  *
  * Note: __O_SYNC must never be used directly.
  */
-#define __O_SYNC	0x800000
+#define __O_SYNC	0040000000
 #define O_SYNC		(__O_SYNC|O_DSYNC)
 
-#define O_PATH		0x1000000
-#define __O_TMPFILE	0x2000000
-#define O_REGULAR	0x4000000
+#define O_PATH		0100000000
+#define __O_TMPFILE	0200000000
+#define O_REGULAR	0400000000
 
 #define F_GETOWN	5	/*  for sockets. */
 #define F_SETOWN	6	/*  for sockets. */
-- 
2.52.0

Following the convention in include/uapi/asm-generic/fcntl.h and other
architecture specific arch/*/include/uapi/asm/fcntl.h files.

Signed-off-by: Dorjoy Chowdhury <dorjoychy111@gmail.com>
---
 arch/mips/include/uapi/asm/fcntl.h | 22 +++++++++++-----------
 1 file changed, 11 insertions(+), 11 deletions(-)

diff --git a/arch/mips/include/uapi/asm/fcntl.h b/arch/mips/include/uapi/asm/fcntl.h
index 0369a38e3d4f..6aa3f49df17e 100644
--- a/arch/mips/include/uapi/asm/fcntl.h
+++ b/arch/mips/include/uapi/asm/fcntl.h
@@ -11,15 +11,15 @@
 
 #include <asm/sgidefs.h>
 
-#define O_APPEND	0x0008
-#define O_DSYNC		0x0010	/* used to be O_SYNC, see below */
-#define O_NONBLOCK	0x0080
-#define O_CREAT		0x0100	/* not fcntl */
-#define O_TRUNC		0x0200	/* not fcntl */
-#define O_EXCL		0x0400	/* not fcntl */
-#define O_NOCTTY	0x0800	/* not fcntl */
-#define FASYNC		0x1000	/* fcntl, for BSD compatibility */
-#define O_LARGEFILE	0x2000	/* allow large file opens */
+#define O_APPEND	0000010
+#define O_DSYNC		0000020	/* used to be O_SYNC, see below */
+#define O_NONBLOCK	0000200
+#define O_CREAT		0000400	/* not fcntl */
+#define O_TRUNC		0001000	/* not fcntl */
+#define O_EXCL		0002000	/* not fcntl */
+#define O_NOCTTY	0004000	/* not fcntl */
+#define FASYNC		0010000	/* fcntl, for BSD compatibility */
+#define O_LARGEFILE	0020000	/* allow large file opens */
 /*
  * Before Linux 2.6.33 only O_DSYNC semantics were implemented, but using
  * the O_SYNC flag.  We continue to use the existing numerical value
@@ -33,9 +33,9 @@
  *
  * Note: __O_SYNC must never be used directly.
  */
-#define __O_SYNC	0x4000
+#define __O_SYNC	0040000
 #define O_SYNC		(__O_SYNC|O_DSYNC)
-#define O_DIRECT	0x8000	/* direct disk access hint */
+#define O_DIRECT	0100000	/* direct disk access hint */
 
 #define F_GETLK		14
 #define F_SETLK		6
-- 
2.52.0