LibC: Implement getgrent_r

Userland/Libraries/LibC/grp.cpp

@@ -20,12 +20,6 @@ extern "C" {
 
 static FILE* s_stream = nullptr;
 static unsigned s_line_number = 0;
-static struct group s_group;
-
-static String s_name;
-static String s_passwd;
-static Vector<String> s_members;
-static Vector<char const*> s_members_ptrs;
 
 void setgrent()
 {
@@ -71,67 +65,120 @@ struct group* getgrnam(char const* name)
     return nullptr;
 }
 
-static bool parse_grpdb_entry(String const& line)
+static bool parse_grpdb_entry(char* buffer, size_t buffer_size, struct group& group_entry)
 {
-    auto parts = line.split_view(':', SplitBehavior::KeepEmpty);
+    size_t line_length = strlen(buffer);
+
+    for (size_t i = 0; i < line_length; ++i) {
+        auto& ch = buffer[i];
+        if (ch == '\r' || ch == '\n')
+            line_length = i;
+        if (ch == ':' || ch == '\r' || ch == '\n')
+            ch = '\0';
+    }
+
+    auto line = StringView { buffer, line_length };
+    auto parts = line.split_view('\0', SplitBehavior::KeepEmpty);
     if (parts.size() != 4) {
-        warnln("getgrent(): Malformed entry on line {}: '{}' has {} parts", s_line_number, line, parts.size());
+        warnln("parse_grpdb_entry(): Malformed entry on line {}: '{}' has {} parts", s_line_number, line, parts.size());
         return false;
     }
 
-    s_name = parts[0];
-    s_passwd = parts[1];
-
+    auto name = parts[0];
+    auto passwd = parts[1];
     auto& gid_string = parts[2];
-    String members_string = parts[3];
+    StringView members_string = parts[3];
 
     auto gid = gid_string.to_uint();
     if (!gid.has_value()) {
-        warnln("getgrent(): Malformed GID on line {}", s_line_number);
+        warnln("parse_grpdb_entry(): Malformed GID on line {}", s_line_number);
         return false;
     }
 
-    s_members = members_string.split(',');
-    s_members_ptrs.clear_with_capacity();
-    s_members_ptrs.ensure_capacity(s_members.size() + 1);
-    for (auto& member : s_members) {
-        s_members_ptrs.append(member.characters());
+    // Generate table of members pointers.
+    Vector<char const*> members_ptrs;
+    auto members = members_string.split_view(',');
+    members_ptrs.clear_with_capacity();
+    members_ptrs.ensure_capacity(members.size() + 1);
+    for (auto& member : members) {
+        members_ptrs.append(member.characters_without_null_termination());
+    }
+    members_ptrs.append(nullptr);
+
+    // Convert remaining commas to null terminators. Last gr_mem entry uses the whole line's null terminator.
+    // 3 for 3 null terminators.
+    size_t members_position = name.length() + passwd.length() + gid_string.length() + 3;
+    for (size_t i = members_position; i < line_length; i++)
+        if (buffer[i] == ',')
+            buffer[i] = '\0';
+
+    // Must have room at the end of the buffer for the new table.
+    // Remaining space is one byte past null terminator generated by original line.
+    size_t bytes_used = line_length + 1;
+    size_t ptrs_size = sizeof(char const*) * members_ptrs.size();
+
+    if (bytes_used + ptrs_size < buffer_size) {
+        char* buffer_remaining = buffer + bytes_used;
+        memcpy(buffer_remaining, members_ptrs.data(), ptrs_size);
+
+        group_entry.gr_gid = gid.value();
+        group_entry.gr_name = const_cast<char*>(name.characters_without_null_termination());
+        group_entry.gr_passwd = const_cast<char*>(passwd.characters_without_null_termination());
+        group_entry.gr_mem = reinterpret_cast<char**>(buffer_remaining);
+
+        return true;
+    } else {
+        warnln("parse_grpdb_entry(): Provided buffer too small to fit table for gr_mem");
+        errno = ERANGE;
+        return false;
     }
-    s_members_ptrs.append(nullptr);
-
-    s_group.gr_gid = gid.value();
-    s_group.gr_name = const_cast<char*>(s_name.characters());
-    s_group.gr_passwd = const_cast<char*>(s_passwd.characters());
-    s_group.gr_mem = const_cast<char**>(s_members_ptrs.data());
-
-    return true;
 }
 
 struct group* getgrent()
+{
+    static struct group group_entry;
+    static char buffer[1024];
+    struct group* result;
+    if (getgrent_r(&group_entry, buffer, sizeof(buffer), &result) < 0)
+        return nullptr;
+    return result;
+}
+
+int getgrent_r(struct group* group_buf, char* buffer, size_t buffer_size, struct group** group_entry_ptr)
 {
     if (!s_stream)
         setgrent();
 
     while (true) {
-        if (!s_stream || feof(s_stream))
-            return nullptr;
+        if (!s_stream || feof(s_stream)) {
+            errno = EIO;
+            return -1;
+        }
 
         if (ferror(s_stream)) {
-            warnln("getgrent(): Read error: {}", strerror(ferror(s_stream)));
-            return nullptr;
+            warnln("getgrent_r(): Read error: {}", strerror(ferror(s_stream)));
+            errno = EIO;
+            return -1;
         }
 
-        char buffer[1024];
         ++s_line_number;
-        char* s = fgets(buffer, sizeof(buffer), s_stream);
+        char* s = fgets(buffer, buffer_size, s_stream);
 
         // Silently tolerate an empty line at the end.
-        if ((!s || !s[0]) && feof(s_stream))
-            return nullptr;
+        if ((!s || !s[0]) && feof(s_stream)) {
+            *group_entry_ptr = nullptr;
+            return 0;
+        }
+
+        if (strlen(s) == buffer_size - 1) {
+            errno = ERANGE;
+            return -1;
+        }
 
-        String line(s, Chomp);
-        if (parse_grpdb_entry(line))
-            return &s_group;
+        if (parse_grpdb_entry(buffer, buffer_size, *group_buf)) {
+            *group_entry_ptr = group_buf;
+            return 0;
+        }
         // Otherwise, proceed to the next line.
     }
 }

Userland/Libraries/LibC/grp.h

@@ -21,6 +21,7 @@ struct group {
 };
 
 struct group* getgrent(void);
+int getgrent_r(struct group* group_buf, char* buffer, size_t buffer_size, struct group** group_entry_ptr);
 void setgrent(void);
 void endgrent(void);
 struct group* getgrnam(char const* name);