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

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
index 5a9cfde5fc288c914ac607fa85a5c97d881b84e6..9a9bb395359c2eed848351d31fe8682717a3404e 100644 (file)
--- 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
index 26f4f05b52efad21f15010ae8ec4377c272cebfd..c797480cbd6f3d6f924ddb4357f405247f7dbf5f 100644 (file)
--- 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
index 0fc8188be31a46b3f46b6bd512817070e198d2e7..7b2eccb541f2cbb1006ca1e5206fbbc1c5872ee7 100644 (file)
--- a/fs/open.c
+++ b/fs/open.c
@@ -645,8 +645,8 @@ retry_deleg:
        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 @@ out:
        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 @@ out:
        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
index 33f06de090ea082d627da0077ce3815703a99c9d..df0d1e818a6e22066a0b119f48a7b97068b83741 100644 (file)
--- 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
index 16c3c23076e25b42609362ce80a73ab42cf6ff7d..35173bef7c00d59329d443e5602b09f3a801548b 100644 (file)
--- 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
index 7b930edfe461d0d6529a70a67ae6f834d1c786f5..af6925d8599b9b2aba17bb26e05792e2250a8f89 100644 (file)
--- 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)