stat/fstat/statx: retrieve file permissions from metadata

Instead of hardcoding file permission bits, retrieve them from the
file metadata.
With this change, the execute permission bit is set when the user
program invokes stat() on the executable file; this is required in
order to avoid "BinaryNotMarkedExecutable" errors when running
tigerbeetle (https://github.com/tigerbeetle/tigerbeetle).

src/unix/filesystem.c

@@ -20,24 +20,40 @@ sysreturn sysreturn_from_fs_status_value(status s)
     return rv;
 }
 
-u16 file_mode_from_type(int type)
+u16 stat_mode(process p, int type, tuple meta)
 {
+    u16 mode;
     switch (type) {
     case FDESC_TYPE_REGULAR:
-        return S_IFREG | 0644;
+        mode = S_IFREG;
+        break;
     case FDESC_TYPE_DIRECTORY:
-        return S_IFDIR | 0777;
+        mode = S_IFDIR;
+        break;
     case FDESC_TYPE_STDIO:
     case FDESC_TYPE_SPECIAL:    /* assuming only character devices */
-        return S_IFCHR;
+        mode = S_IFCHR;
+        break;
     case FDESC_TYPE_SOCKET:
-        return S_IFSOCK;
+        mode = S_IFSOCK;
+        break;
     case FDESC_TYPE_PIPE:
-        return S_IFIFO;
+        mode = S_IFIFO;
+        break;
     case FDESC_TYPE_SYMLINK:
-        return S_IFLNK;
+        mode = S_IFLNK;
+        break;
+    default:
+        return 0;
     }
-    return 0;
+    u32 perms = file_meta_perms(p, meta);
+    if (perms & ACCESS_PERM_READ)
+        mode |= 0444;
+    if (perms & ACCESS_PERM_WRITE)
+        mode |= 0222;
+    if (perms & ACCESS_PERM_EXEC)
+        mode |= 0111;
+    return mode;
 }
 
 void file_readahead(file f, u64 offset, u64 len)
@@ -355,7 +371,7 @@ static sysreturn statx_internal(filesystem fs, int type, tuple n, fsfile f, stru
     if (!validate_user_memory(statxbuf, sizeof(struct rlimit), true) || context_set_err(ctx))
         return -EFAULT;
     zero(statxbuf, sizeof(*statxbuf));
-    statxbuf->stx_mode = file_mode_from_type(type);
+    statxbuf->stx_mode = stat_mode(current->p, type, n);
     statxbuf->stx_mask = STATX_TYPE | STATX_MODE;
     switch (type) {
     case FDESC_TYPE_REGULAR:

src/unix/filesystem.h

@@ -24,7 +24,7 @@
 
 sysreturn sysreturn_from_fs_status_value(status s);
 
-u16 file_mode_from_type(int type);
+u16 stat_mode(process p, int type, tuple meta);
 
 /* Perform read-ahead following a userspace read request.
  * offset and len arguments refer to the byte range being read from userspace,

src/unix/syscall.c

@@ -1447,7 +1447,7 @@ sysreturn openat(int dirfd, const char *name, int flags, int mode)
 static void fill_stat(int type, filesystem fs, fsfile f, tuple n, struct stat *s)
 {
     zero(s, sizeof(struct stat));
-    s->st_mode = file_mode_from_type(type);
+    s->st_mode = stat_mode(current->p, type, n);
     switch (type) {
     case FDESC_TYPE_REGULAR:
         if (f) {

test/runtime/symlink.c

@@ -91,15 +91,13 @@ int main(int argc, char **argv)
 
     test_assert((faccessat(AT_FDCWD, "link", F_OK, AT_SYMLINK_NOFOLLOW) == 0));
     test_assert((faccessat(AT_FDCWD, "link", R_OK|W_OK, AT_SYMLINK_NOFOLLOW) == 0));
-    test_assert((faccessat(AT_FDCWD, "link", X_OK, AT_SYMLINK_NOFOLLOW) == -1 && (errno == EACCES)));
     test_assert((faccessat(AT_FDCWD, "link", F_OK, 0) == -1) && (errno == ENOENT));
 
     fd = open("target", O_RDWR | O_CREAT, S_IRWXU);
     test_assert(fd >= 0);
     close(fd);
 
     test_assert((faccessat(AT_FDCWD, "link", F_OK, 0) == 0));
-    test_assert((faccessat(AT_FDCWD, "link", X_OK, AT_SYMLINK_NOFOLLOW) == -1 && (errno == EACCES)));
     test_assert((faccessat(AT_FDCWD, "link", X_OK|R_OK|W_OK, 0) == 0));
     test_assert((access("link", F_OK) == 0));
     test_assert((access("link", X_OK|R_OK|W_OK) == 0));