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fs: add do_faccessat() helper and ksys_access() wrapper; remove in-kernel calls to syscall

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Using the fs-internal do_faccessat() helper allows us to get rid of
fs-internal calls to the sys_faccessat() syscall.

Introducing the ksys_access() wrapper allows us to avoid the in-kernel
calls to the sys_access() syscall. The ksys_ prefix denotes that this
function is meant as a drop-in replacement for the syscall. In
particular, it uses the same calling convention as sys_access().

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>
This commit is contained in:
Dominik Brodowski 2018-03-11 11:34:54 +01:00
parent 03450e271a
commit cbfe20f565
4 changed files with 17 additions and 3 deletions
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1
fs/internal.h
View File

@ -119,6 +119,7 @@ extern struct file *do_filp_open(int dfd, struct filename *pathname,
extern struct file *do_file_open_root(struct dentry *, struct vfsmount *,
const char *, const struct open_flags *);
long do_faccessat(int dfd, const char __user *filename, int mode);
int do_fchmodat(int dfd, const char __user *filename, umode_t mode);
extern int open_check_o_direct(struct file *f);

9
fs/open.c
View File

@ -350,7 +350,7 @@ SYSCALL_DEFINE4(fallocate, int, fd, int, mode, loff_t, offset, loff_t, len)
* We do this by temporarily clearing all FS-related capabilities and
* switching the fsuid/fsgid around to the real ones.
*/
SYSCALL_DEFINE3(faccessat, int, dfd, const char __user *, filename, int, mode)
long do_faccessat(int dfd, const char __user *filename, int mode)
{
const struct cred *old_cred;
struct cred *override_cred;
@ -426,9 +426,14 @@ SYSCALL_DEFINE3(faccessat, int, dfd, const char __user *, filename, int, mode)
return res;
}
SYSCALL_DEFINE3(faccessat, int, dfd, const char __user *, filename, int, mode)
{
return do_faccessat(dfd, filename, mode);
}
SYSCALL_DEFINE2(access, const char __user *, filename, int, mode)
{
return sys_faccessat(AT_FDCWD, filename, mode);
return do_faccessat(AT_FDCWD, filename, mode);
}
int ksys_chdir(const char __user *filename)

7
include/linux/syscalls.h
View File

@ -1014,4 +1014,11 @@ static inline int ksys_chmod(const char __user *filename, umode_t mode)
return do_fchmodat(AT_FDCWD, filename, mode);
}
extern long do_faccessat(int dfd, const char __user *filename, int mode);
static inline long ksys_access(const char __user *filename, int mode)
{
return do_faccessat(AT_FDCWD, filename, mode);
}
#endif

3
init/main.c
View File

@ -1087,7 +1087,8 @@ static noinline void __init kernel_init_freeable(void)
if (!ramdisk_execute_command)
ramdisk_execute_command = "/init";
if (sys_access((const char __user *) ramdisk_execute_command, 0) != 0) {
if (ksys_access((const char __user *)
ramdisk_execute_command, 0) != 0) {
ramdisk_execute_command = NULL;
prepare_namespace();
}