kernel+libc: Add access()

kernel/src/sys/stat.cpp

@@ -1,6 +1,7 @@
 #include "memory/MemoryManager.h"
 #include "sys/Syscall.h"
 #include "thread/Scheduler.h"
+#include <bits/access.h>
 #include <bits/atfile.h>
 #include <bits/modes.h>
 #include <bits/struct_stat.h>
@@ -49,3 +50,33 @@ Result<u64> sys_fstatat(Registers*, SyscallArgs args)
 
     return 0;
 }
+
+Result<u64> sys_faccessat(Registers*, SyscallArgs args)
+{
+    int dirfd = (int)args[0];
+    auto path = TRY(MemoryManager::strdup_from_user(args[1]));
+    int amode = (int)args[2];
+    int flags = (int)args[3];
+
+    Credentials creds;
+
+    auto* current = Scheduler::current();
+
+    if (flags & AT_EACCESS) creds = current->auth;
+    else
+    {
+        auto auth = current->auth;
+        creds.euid = auth.uid;
+        creds.egid = auth.gid;
+    }
+
+    auto inode = TRY(current->resolve_atfile(dirfd, path, false, true));
+
+    if ((amode & R_OK) && !VFS::can_read(inode, creds)) return err(EACCES);
+    if ((amode & W_OK) && !VFS::can_write(inode, creds)) return err(EACCES);
+    if ((amode & X_OK) && !VFS::can_execute(inode, creds)) return err(EACCES);
+
+    // Either all checks succeeded, or amode == F_OK and the file exists, since resolve_atfile() would have failed
+    // otherwise.
+    return 0;
+}

libc/include/bits/access.h

@@ -0,0 +1,12 @@
+/* bits/access.h: Definitions for the access() function. */
+
+#ifndef _BITS_ACCESS_H
+#define _BITS_ACCESS_H
+
+#define R_OK 1
+#define W_OK 2
+#define X_OK 4
+
+#define F_OK 0
+
+#endif

libc/include/bits/atfile.h

@@ -10,4 +10,6 @@
 
 #define AT_REMOVEDIR 1
 
+#define AT_EACCESS 1
+
 #endif

libc/include/unistd.h

@@ -6,6 +6,7 @@
 #define __need_NULL
 #include <stddef.h>
 
+#include <bits/access.h>
 #include <bits/seek.h>
 #include <stdint.h>
 #include <sys/types.h>
@@ -151,6 +152,15 @@ extern "C"
     /* Create a hard link relative to a file descriptor. */
     int linkat(int olddirfd, const char* oldpath, int newdirfd, const char* newpath, int flags);
 
+    /* Check for a file's accessibility. */
+    int access(const char* path, int amode);
+
+    /* Check for a file's accessibility using the effective user and group IDs. */
+    int eaccess(const char* path, int amode);
+
+    /* Check for a file's accessibility relative to a file descriptor. */
+    int faccessat(int dirfd, const char* path, int amode, int flags);
+
 #ifdef __cplusplus
 }
 #endif

libc/src/unistd.cpp

@@ -442,4 +442,22 @@ extern "C"
         long rc = syscall(SYS_linkat, olddirfd, oldpath, newdirfd, newpath, flags);
         __errno_return(rc, int);
     }
+
+    int access(const char* path, int amode)
+    {
+        long rc = syscall(SYS_faccessat, AT_FDCWD, path, amode, 0);
+        __errno_return(rc, int);
+    }
+
+    int eaccess(const char* path, int amode)
+    {
+        long rc = syscall(SYS_faccessat, AT_FDCWD, path, amode, AT_EACCESS);
+        __errno_return(rc, int);
+    }
+
+    int faccessat(int dirfd, const char* path, int amode, int flags)
+    {
+        long rc = syscall(SYS_faccessat, dirfd, path, amode, flags);
+        __errno_return(rc, int);
+    }
 }

libluna/include/luna/Syscall.h

@@ -5,7 +5,7 @@
         _e(lseek) _e(mkdir) _e(execve) _e(fork) _e(waitpid) _e(getppid) _e(fcntl) _e(getdents) _e(getuid) _e(geteuid)  \
             _e(getgid) _e(getegid) _e(setuid) _e(setgid) _e(seteuid) _e(setegid) _e(fchmodat) _e(fchownat) _e(ioctl)   \
                 _e(fstatat) _e(chdir) _e(getcwd) _e(unlinkat) _e(uname) _e(sethostname) _e(dup2) _e(pipe) _e(mount)    \
-                    _e(umount) _e(pstat) _e(getrusage) _e(symlinkat) _e(readlinkat) _e(umask) _e(linkat)
+                    _e(umount) _e(pstat) _e(getrusage) _e(symlinkat) _e(readlinkat) _e(umask) _e(linkat) _e(faccessat)
 
 enum Syscalls
 {