Fix F_DUPFD crash when there is no space in file table

src/libos/src/fs/file_table.rs

@@ -33,17 +33,23 @@ impl FileTable {
             if min_fd >= table.len() {
                 let expand_size = min_fd - table.len() + 1;
                 for _ in 0..expand_size {
-                    table.push(None)
+                    table.push(None);
                 }
             }
 
-            table
+            let free_fd = table
                 .iter()
                 .enumerate()
                 .skip(min_fd as usize)
-                .find(|&(idx, opt)| opt.is_none())
+                .find(|&(idx, opt)| opt.is_none());
-                .unwrap()
+
-                .0
+            if let Some((index, _)) = free_fd {
+                index
+            } else {
+                // Span table when no free fd is found
+                table.push(None);
+                table.len() - 1
+            }
         } as FileDesc;
 
         self.put_at(min_free_fd, file_ref, close_on_spawn);

test/fcntl/main.c

@@ -69,6 +69,12 @@ static int __fcntl_getlk_and_setlk(int fd, int open_flags) {
     return 0;
 }
 
+static int __fcntl_dupfd(int fd, int open_flags) {
+    if (fcntl(fd, F_DUPFD, 0) < 0)
+        THROW_ERROR("failed to duplicate the fd");
+    return 0;
+}
+
 typedef int(*test_fcntl_func_t)(int fd, int open_flags);
 
 static int test_fcntl_framework(test_fcntl_func_t fn) {
@@ -104,6 +110,10 @@ static int test_getlk_and_setlk() {
     return test_fcntl_framework(__fcntl_getlk_and_setlk);
 }
 
+static int test_fcntl_dupfd() {
+    return test_fcntl_framework(__fcntl_dupfd);
+}
+
 // ============================================================================
 // Test suite
 // ============================================================================
@@ -112,6 +122,7 @@ static test_case_t test_cases[] = {
     TEST_CASE(test_fcntl_getfl),
     TEST_CASE(test_fcntl_setfl),
     TEST_CASE(test_getlk_and_setlk),
+    TEST_CASE(test_fcntl_dupfd),
 };
 
 int main() {