fs: add do_fchownat(), ksys_fchown() helpers and ksys_{,l}chown() wrappers

Dominik Brodowski · Dominik Brodowski · commit 55731b3cda3a · 2018-04-02T20:15:59.000+02:00
Using the fs-interal do_fchownat() wrapper allows us to get rid of fs-internal calls to the sys_fchownat() syscall. Introducing the ksys_fchown() helper and the ksys_{,}chown() wrappers allows us to avoid the in-kernel calls to the sys_{,l,f}chown() syscalls. The ksys_ prefix denotes that these functions are meant as a drop-in replacement for the syscalls. In particular, they use the same calling convention as sys_{,l,f}chown(). This patch is part of a series which removes in-kernel calls to syscalls. On this basis, the syscall entry path can be streamlined. For details, see http://lkml.kernel.org/r/20180325162527.GA17492@light.dominikbrodowski.net Cc: Al Viro <viro@zeniv.linux.org.uk> Cc: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Dominik Brodowski <linux@dominikbrodowski.net>
diff --git a/arch/s390/kernel/compat_linux.c b/arch/s390/kernel/compat_linux.c
@@ -89,18 +89,18 @@
 COMPAT_SYSCALL_DEFINE3(s390_chown16, const char __user *, filename,
 		       u16, user, u16, group)
 {
-	return sys_chown(filename, low2highuid(user), low2highgid(group));
+	return ksys_chown(filename, low2highuid(user), low2highgid(group));
 }
 
 COMPAT_SYSCALL_DEFINE3(s390_lchown16, const char __user *,
 		       filename, u16, user, u16, group)
 {
-	return sys_lchown(filename, low2highuid(user), low2highgid(group));
+	return ksys_lchown(filename, low2highuid(user), low2highgid(group));
 }
 
 COMPAT_SYSCALL_DEFINE3(s390_fchown16, unsigned int, fd, u16, user, u16, group)
 {
-	return sys_fchown(fd, low2highuid(user), low2highgid(group));
+	return ksys_fchown(fd, low2highuid(user), low2highgid(group));
 }
 
 COMPAT_SYSCALL_DEFINE2(s390_setregid16, u16, rgid, u16, egid)
diff --git a/fs/internal.h b/fs/internal.h
@@ -121,6 +121,8 @@ extern struct file *do_file_open_root(struct dentry *, struct vfsmount *,
 
 long do_faccessat(int dfd, const char __user *filename, int mode);
 int do_fchmodat(int dfd, const char __user *filename, umode_t mode);
+int do_fchownat(int dfd, const char __user *filename, uid_t user, gid_t group,
+		int flag);
 
 extern int open_check_o_direct(struct file *f);
 extern int vfs_open(const struct path *, struct file *, const struct cred *);
diff --git a/fs/open.c b/fs/open.c
@@ -645,8 +645,8 @@ static int chown_common(const struct path *path, uid_t user, gid_t group)
 	return error;
 }
 
-SYSCALL_DEFINE5(fchownat, int, dfd, const char __user *, filename, uid_t, user,
-		gid_t, group, int, flag)
+int do_fchownat(int dfd, const char __user *filename, uid_t user, gid_t group,
+		int flag)
 {
 	struct path path;
 	int error = -EINVAL;
@@ -677,18 +677,24 @@ SYSCALL_DEFINE5(fchownat, int, dfd, const char __user *, filename, uid_t, user,
 	return error;
 }
 
+SYSCALL_DEFINE5(fchownat, int, dfd, const char __user *, filename, uid_t, user,
+		gid_t, group, int, flag)
+{
+	return do_fchownat(dfd, filename, user, group, flag);
+}
+
 SYSCALL_DEFINE3(chown, const char __user *, filename, uid_t, user, gid_t, group)
 {
-	return sys_fchownat(AT_FDCWD, filename, user, group, 0);
+	return do_fchownat(AT_FDCWD, filename, user, group, 0);
 }
 
 SYSCALL_DEFINE3(lchown, const char __user *, filename, uid_t, user, gid_t, group)
 {
-	return sys_fchownat(AT_FDCWD, filename, user, group,
-			    AT_SYMLINK_NOFOLLOW);
+	return do_fchownat(AT_FDCWD, filename, user, group,
+			   AT_SYMLINK_NOFOLLOW);
 }
 
-SYSCALL_DEFINE3(fchown, unsigned int, fd, uid_t, user, gid_t, group)
+int ksys_fchown(unsigned int fd, uid_t user, gid_t group)
 {
 	struct fd f = fdget(fd);
 	int error = -EBADF;
@@ -708,6 +714,11 @@ SYSCALL_DEFINE3(fchown, unsigned int, fd, uid_t, user, gid_t, group)
 	return error;
 }
 
+SYSCALL_DEFINE3(fchown, unsigned int, fd, uid_t, user, gid_t, group)
+{
+	return ksys_fchown(fd, user, group);
+}
+
 int open_check_o_direct(struct file *f)
 {
 	/* NB: we're sure to have correct a_ops only after f_op->open */
diff --git a/include/linux/syscalls.h b/include/linux/syscalls.h
@@ -954,6 +954,7 @@ int ksys_chroot(const char __user *filename);
 ssize_t ksys_write(unsigned int fd, const char __user *buf, size_t count);
 int ksys_chdir(const char __user *filename);
 int ksys_fchmod(unsigned int fd, umode_t mode);
+int ksys_fchown(unsigned int fd, uid_t user, gid_t group);
 
 /*
  * The following kernel syscall equivalents are just wrappers to fs-internal
@@ -1021,4 +1022,20 @@ static inline long ksys_access(const char __user *filename, int mode)
 	return do_faccessat(AT_FDCWD, filename, mode);
 }
 
+extern int do_fchownat(int dfd, const char __user *filename, uid_t user,
+		       gid_t group, int flag);
+
+static inline long ksys_chown(const char __user *filename, uid_t user,
+			      gid_t group)
+{
+	return do_fchownat(AT_FDCWD, filename, user, group, 0);
+}
+
+static inline long ksys_lchown(const char __user *filename, uid_t user,
+			       gid_t group)
+{
+	return do_fchownat(AT_FDCWD, filename, user, group,
+			     AT_SYMLINK_NOFOLLOW);
+}
+
 #endif
diff --git a/init/initramfs.c b/init/initramfs.c
@@ -343,7 +343,7 @@ static int __init do_name(void)
 			wfd = sys_open(collected, openflags, mode);
 
 			if (wfd >= 0) {
-				sys_fchown(wfd, uid, gid);
+				ksys_fchown(wfd, uid, gid);
 				ksys_fchmod(wfd, mode);
 				if (body_len)
 					sys_ftruncate(wfd, body_len);
@@ -353,14 +353,14 @@ static int __init do_name(void)
 		}
 	} else if (S_ISDIR(mode)) {
 		ksys_mkdir(collected, mode);
-		sys_chown(collected, uid, gid);
+		ksys_chown(collected, uid, gid);
 		ksys_chmod(collected, mode);
 		dir_add(collected, mtime);
 	} else if (S_ISBLK(mode) || S_ISCHR(mode) ||
 		   S_ISFIFO(mode) || S_ISSOCK(mode)) {
 		if (maybe_link() == 0) {
 			ksys_mknod(collected, mode, rdev);
-			sys_chown(collected, uid, gid);
+			ksys_chown(collected, uid, gid);
 			ksys_chmod(collected, mode);
 			do_utime(collected, mtime);
 		}
@@ -393,7 +393,7 @@ static int __init do_symlink(void)
 	collected[N_ALIGN(name_len) + body_len] = '\0';
 	clean_path(collected, 0);
 	ksys_symlink(collected + N_ALIGN(name_len), collected);
-	sys_lchown(collected, uid, gid);
+	ksys_lchown(collected, uid, gid);
 	do_utime(collected, mtime);
 	state = SkipIt;
 	next_state = Reset;
diff --git a/kernel/uid16.c b/kernel/uid16.c
@@ -22,17 +22,17 @@
 
 SYSCALL_DEFINE3(chown16, const char __user *, filename, old_uid_t, user, old_gid_t, group)
 {
-	return sys_chown(filename, low2highuid(user), low2highgid(group));
+	return ksys_chown(filename, low2highuid(user), low2highgid(group));
 }
 
 SYSCALL_DEFINE3(lchown16, const char __user *, filename, old_uid_t, user, old_gid_t, group)
 {
-	return sys_lchown(filename, low2highuid(user), low2highgid(group));
+	return ksys_lchown(filename, low2highuid(user), low2highgid(group));
 }
 
 SYSCALL_DEFINE3(fchown16, unsigned int, fd, old_uid_t, user, old_gid_t, group)
 {
-	return sys_fchown(fd, low2highuid(user), low2highgid(group));
+	return ksys_fchown(fd, low2highuid(user), low2highgid(group));
 }
 
 SYSCALL_DEFINE2(setregid16, old_gid_t, rgid, old_gid_t, egid)

Original file line number	Diff line number	Diff line change
`@@ -89,18 +89,18 @@`
`89`	`89`	`COMPAT_SYSCALL_DEFINE3(s390_chown16, const char __user *, filename,`
`90`	`90`	`u16, user, u16, group)`
`91`	`91`	`{`
`92`		`- return sys_chown(filename, low2highuid(user), low2highgid(group));`
	`92`	`+ return ksys_chown(filename, low2highuid(user), low2highgid(group));`
`93`	`93`	`}`
`94`	`94`
`95`	`95`	`COMPAT_SYSCALL_DEFINE3(s390_lchown16, const char __user *,`
`96`	`96`	`filename, u16, user, u16, group)`
`97`	`97`	`{`
`98`		`- return sys_lchown(filename, low2highuid(user), low2highgid(group));`
	`98`	`+ return ksys_lchown(filename, low2highuid(user), low2highgid(group));`
`99`	`99`	`}`
`100`	`100`
`101`	`101`	`COMPAT_SYSCALL_DEFINE3(s390_fchown16, unsigned int, fd, u16, user, u16, group)`
`102`	`102`	`{`
`103`		`- return sys_fchown(fd, low2highuid(user), low2highgid(group));`
	`103`	`+ return ksys_fchown(fd, low2highuid(user), low2highgid(group));`
`104`	`104`	`}`
`105`	`105`
`106`	`106`	`COMPAT_SYSCALL_DEFINE2(s390_setregid16, u16, rgid, u16, egid)`
Original file line number	Diff line number	Diff line change
`@@ -645,8 +645,8 @@ static int chown_common(const struct path *path, uid_t user, gid_t group)`
`645`	`645`	`return error;`
`646`	`646`	`}`
`647`	`647`
`648`		`-SYSCALL_DEFINE5(fchownat, int, dfd, const char __user *, filename, uid_t, user,`
`649`		`- gid_t, group, int, flag)`
	`648`	`+int do_fchownat(int dfd, const char __user *filename, uid_t user, gid_t group,`
	`649`	`+ int flag)`
`650`	`650`	`{`
`651`	`651`	`struct path path;`
`652`	`652`	`int error = -EINVAL;`
`@@ -677,18 +677,24 @@ SYSCALL_DEFINE5(fchownat, int, dfd, const char __user *, filename, uid_t, user,`
`677`	`677`	`return error;`
`678`	`678`	`}`
`679`	`679`
	`680`	`+SYSCALL_DEFINE5(fchownat, int, dfd, const char __user *, filename, uid_t, user,`
	`681`	`+ gid_t, group, int, flag)`
	`682`	`+{`
	`683`	`+ return do_fchownat(dfd, filename, user, group, flag);`
	`684`	`+}`
	`685`	`+`
`680`	`686`	`SYSCALL_DEFINE3(chown, const char __user *, filename, uid_t, user, gid_t, group)`
`681`	`687`	`{`
`682`		`- return sys_fchownat(AT_FDCWD, filename, user, group, 0);`
	`688`	`+ return do_fchownat(AT_FDCWD, filename, user, group, 0);`
`683`	`689`	`}`
`684`	`690`
`685`	`691`	`SYSCALL_DEFINE3(lchown, const char __user *, filename, uid_t, user, gid_t, group)`
`686`	`692`	`{`
`687`		`- return sys_fchownat(AT_FDCWD, filename, user, group,`
`688`		`- AT_SYMLINK_NOFOLLOW);`
	`693`	`+ return do_fchownat(AT_FDCWD, filename, user, group,`
	`694`	`+ AT_SYMLINK_NOFOLLOW);`
`689`	`695`	`}`
`690`	`696`
`691`		`-SYSCALL_DEFINE3(fchown, unsigned int, fd, uid_t, user, gid_t, group)`
	`697`	`+int ksys_fchown(unsigned int fd, uid_t user, gid_t group)`
`692`	`698`	`{`
`693`	`699`	`struct fd f = fdget(fd);`
`694`	`700`	`int error = -EBADF;`
`@@ -708,6 +714,11 @@ SYSCALL_DEFINE3(fchown, unsigned int, fd, uid_t, user, gid_t, group)`
`708`	`714`	`return error;`
`709`	`715`	`}`
`710`	`716`
	`717`	`+SYSCALL_DEFINE3(fchown, unsigned int, fd, uid_t, user, gid_t, group)`
	`718`	`+{`
	`719`	`+ return ksys_fchown(fd, user, group);`
	`720`	`+}`
	`721`	`+`
`711`	`722`	`int open_check_o_direct(struct file *f)`
`712`	`723`	`{`
`713`	`724`	`/* NB: we're sure to have correct a_ops only after f_op->open */`
Original file line number	Diff line number	Diff line change
`@@ -22,17 +22,17 @@`
`22`	`22`
`23`	`23`	`SYSCALL_DEFINE3(chown16, const char __user *, filename, old_uid_t, user, old_gid_t, group)`
`24`	`24`	`{`
`25`		`- return sys_chown(filename, low2highuid(user), low2highgid(group));`
	`25`	`+ return ksys_chown(filename, low2highuid(user), low2highgid(group));`
`26`	`26`	`}`
`27`	`27`
`28`	`28`	`SYSCALL_DEFINE3(lchown16, const char __user *, filename, old_uid_t, user, old_gid_t, group)`
`29`	`29`	`{`
`30`		`- return sys_lchown(filename, low2highuid(user), low2highgid(group));`
	`30`	`+ return ksys_lchown(filename, low2highuid(user), low2highgid(group));`
`31`	`31`	`}`
`32`	`32`
`33`	`33`	`SYSCALL_DEFINE3(fchown16, unsigned int, fd, old_uid_t, user, old_gid_t, group)`
`34`	`34`	`{`
`35`		`- return sys_fchown(fd, low2highuid(user), low2highgid(group));`
	`35`	`+ return ksys_fchown(fd, low2highuid(user), low2highgid(group));`
`36`	`36`	`}`
`37`	`37`
`38`	`38`	`SYSCALL_DEFINE2(setregid16, old_gid_t, rgid, old_gid_t, egid)`