fs: add do_faccessat() helper and ksys_access() wrapper; remove in-ke…

…rnel 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/[email protected] Cc: Al Viro <[email protected]> Cc: Andrew Morton <[email protected]> Signed-off-by: Dominik Brodowski <[email protected]>
cail · Apr 2, 2018 · cbfe20f · cbfe20f
1 parent 03450e2
commit cbfe20f
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Showing 4 changed files with 17 additions and 3 deletions.
diff --git a/fs/internal.h b/fs/internal.h
@@ -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);

diff --git a/fs/open.c b/fs/open.c
@@ -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)

diff --git a/include/linux/syscalls.h b/include/linux/syscalls.h
@@ -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
diff --git a/init/main.c b/init/main.c
@@ -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();
 	}