storedPlaylist: prevent potential DoS from stored playlist commands

While mpd has always protected against the infinite expansion of the main playlist by limiting its size in memory, however the new storedPlaylist code has never checked for this limit. Malicious (or clumsy) users could repeatedly append songs to stored playlists, causing files to grow increasingly large on disk. Attempting to load extremely large files into memory will require mpd to slurp that all into memory, and ultimately the file would be unusable by mpd because of the configurable playlist size limit. Now we limit stored playlists to the max_playlist_length configuration variable set by the user (default is 16384). We will refuse to append to playlist files if they hit that limit; and also refuse to load more than the specified amount of songs into memory. git-svn-id: https://svn.musicpd.org/mpd/trunk@7154 09075e82-0dd4-0310-85a5-a0d7c8717e4f

storedPlaylist: prevent potential DoS from stored playlist commands
29df7036 · Eric Wong · 3a1b3e38 · 29df7036 · 29df7036 · 29df7036
Commit 29df7036 authored Jan 26, 2008 by Eric Wong
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Showing with 18 additions and 2 deletions

playlist.c src/playlist.c +1 -1

playlist.h src/playlist.h +2 -0

storedPlaylist.c src/storedPlaylist.c +15 -1

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--- a/src/playlist.c
+++ b/src/playlist.c
@@ -58,7 +58,7 @@

 static Playlist playlist;
 static int playlist_state = PLAYLIST_STATE_STOP;
-static int playlist_max_length = DEFAULT_PLAYLIST_MAX_LENGTH;
+int playlist_max_length = DEFAULT_PLAYLIST_MAX_LENGTH;
 static int playlist_stopOnError;
 static int playlist_errorCount;
 static int playlist_queueError;

--- a/src/playlist.h
+++ b/src/playlist.h
@@ -45,6 +45,8 @@ typedef struct _Playlist {

 extern int playlist_saveAbsolutePaths;

+extern int playlist_max_length;
+
 void initPlaylist(void);

 void finishPlaylist(void);

--- a/src/storedPlaylist.c
+++ b/src/storedPlaylist.c
@@ -129,6 +129,9 @@ List *loadStoredPlaylist(int fd, const char *utf8path)
 			insertInListWithoutKey(list, xstrdup(path_max_tmp));
 		} else if (isValidRemoteUtf8Url(s))
 			insertInListWithoutKey(list, xstrdup(s));
+
+		if (list->numberOfNodes >= playlist_max_length)
+			break;
 	}

 	while (fclose(file) && errno == EINTR);
@@ -284,6 +287,7 @@ int appendSongToStoredPlaylistByPath(int fd, const char *utf8path, Song *song)
 {
 	FILE *file;
 	char *s;
+	int nr_songs = 0;
 	char path_max_tmp[MPD_PATH_MAX];
 	char path_max_tmp2[MPD_PATH_MAX];

@@ -291,12 +295,22 @@ int appendSongToStoredPlaylistByPath(int fd, const char *utf8path, Song *song)
 		return -1;
 	utf8_to_fs_playlist_path(path_max_tmp, utf8path);

-	while (!(file = fopen(path_max_tmp, "a")) && errno == EINTR);
+	while (!(file = fopen(path_max_tmp, "a+")) && errno == EINTR);
 	if (file == NULL) {
 		commandError(fd, ACK_ERROR_NO_EXIST, "could not open file "
 		             "\"%s\": %s", path_max_tmp, strerror(errno));
 		return -1;
 	}
+	while (myFgets(path_max_tmp, sizeof(path_max_tmp), file)) {
+		if (path_max_tmp[0] != PLAYLIST_COMMENT &&
+		    (++nr_songs >= playlist_max_length))
+			break;
+	}
+	if (nr_songs >= playlist_max_length) {
+		commandError(fd, ACK_ERROR_PLAYLIST_MAX,
+		             "playlist is at the max size");
+		return -1;
+	}

 	s = utf8_to_fs_charset(path_max_tmp2, get_song_url(path_max_tmp, song));