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    Subject[PATCH 081/109] fs: add do_fchownat(), ksys_fchown() helpers and ksys_{,l}chown() wrappers
    Date
    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>
    ---
    arch/s390/kernel/compat_linux.c | 6 +++---
    fs/internal.h | 2 ++
    fs/open.c | 23 +++++++++++++++++------
    include/linux/syscalls.h | 17 +++++++++++++++++
    init/initramfs.c | 8 ++++----
    kernel/uid16.c | 6 +++---
    6 files changed, 46 insertions(+), 16 deletions(-)

    diff --git a/arch/s390/kernel/compat_linux.c b/arch/s390/kernel/compat_linux.c
    index 5a9cfde5fc28..9a9bb395359c 100644
    --- 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 26f4f05b52ef..c797480cbd6f 100644
    --- 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 0fc8188be31a..7b2eccb541f2 100644
    --- 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
    index 33f06de090ea..df0d1e818a6e 100644
    --- 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 16c3c23076e2..35173bef7c00 100644
    --- 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 7b930edfe461..af6925d8599b 100644
    --- 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)
    --
    2.16.3
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