Commit cbfe20f5 authored by Dominik Brodowski's avatar Dominik Brodowski
Browse files

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

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: default avatarDominik Brodowski <linux@dominikbrodowski.net>
parent 03450e27

fs/internal.h

+1 −0
Original line number Diff line number Diff line
@@ -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);

fs/open.c

+7 −2
Original line number Diff line number Diff line
@@ -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 @@ out: 
	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)

include/linux/syscalls.h

+7 −0
Original line number Diff line number Diff line
@@ -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

init/main.c

+2 −1
Original line number Diff line number Diff line
@@ -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();

	}

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