avformat/hls: Be more picky on extensions

This blocks disallowed extensions from probing
It also requires all available segments to have matching extensions to the format
mpegts is treated independent of the extension

It is recommended to set the whitelists correctly
instead of depending on extensions, but this should help a bit,
and this is easier to backport

Fixes: CVE-2023-6602 II. HLS Force TTY Demuxer
Fixes: CVE-2023-6602 IV. HLS XBIN Demuxer DoS Amplification

The other parts of CVE-2023-6602 have been fixed by prior commits

Found-by: Harvey Phillips of Amazon Element55 (element55)
Signed-off-by: Michael Niedermayer <[email protected]>
(cherry picked from commit 91d96dc8ddaebe0b6cb393f672085e6bfaf15a31)
Signed-off-by: Michael Niedermayer <[email protected]>

diff --git a/doc/demuxers.texi b/doc/demuxers.texi
index 3c15ab9eeec5b51bc89e66a626ce36caa3248463..6c948632712da7755fbc87134e3eb8def6b8165e 100644 (file)
--- a/doc/demuxers.texi
+++ b/doc/demuxers.texi
@@ -327,6 +327,13 @@ segment index to start live streams at (negative values are from the end).
 @item allowed_extensions
 ',' separated list of file extensions that hls is allowed to access.
 
+@item extension_picky
+This blocks disallowed extensions from probing
+It also requires all available segments to have matching extensions to the format
+except mpegts, which is always allowed.
+It is recommended to set the whitelists correctly instead of depending on extensions
+Enabled by default.
+
 @item max_reload
 Maximum number of times a insufficient list is attempted to be reloaded.
 Default value is 1000.

diff --git a/libavformat/hls.c b/libavformat/hls.c
index 650c0dc863ac0a0f18fdea447773d847c14f5257..e94c4f9ae39a6bb4f2aa8554ded2f12cccd863af 100644 (file)
--- a/libavformat/hls.c
+++ b/libavformat/hls.c
@@ -208,6 +208,7 @@ typedef struct HLSContext {
     AVIOInterruptCB *interrupt_callback;
     AVDictionary *avio_opts;
     char *allowed_extensions;
+    int extension_picky;
     int max_reload;
     int http_persistent;
     int http_multiple;
@@ -712,6 +713,40 @@ static int open_url(AVFormatContext *s, AVIOContext **pb, const char *url,
     return ret;
 }
 
+static int test_segment(AVFormatContext *s, const AVInputFormat *in_fmt, struct playlist *pls, struct segment *seg)
+{
+    HLSContext *c = s->priv_data;
+    int matchA = 3;
+    int matchF = 0;
+
+    if (!c->extension_picky)
+        return 0;
+
+    if (strcmp(c->allowed_extensions, "ALL"))
+        matchA =      av_match_ext    (seg->url, c->allowed_extensions)
+                 + 2*(ff_match_url_ext(seg->url, c->allowed_extensions) > 0);
+
+    if (!matchA) {
+        av_log(s, AV_LOG_ERROR, "URL %s is not in allowed_extensions\n", seg->url);
+        return AVERROR_INVALIDDATA;
+    }
+
+    if (in_fmt) {
+        if (in_fmt->extensions) {
+            matchF =      av_match_ext(    seg->url, in_fmt->extensions)
+                     + 2*(ff_match_url_ext(seg->url, in_fmt->extensions) > 0);
+        } else if (!strcmp(in_fmt->name, "mpegts"))
+            matchF = 3;
+
+        if (!(matchA & matchF)) {
+            av_log(s, AV_LOG_ERROR, "detected format extension %s mismatches allowed extensions in url %s\n", in_fmt->extensions ? in_fmt->extensions : "none", seg->url);
+            return AVERROR_INVALIDDATA;
+        }
+    }
+
+    return 0;
+}
+
 static int parse_playlist(HLSContext *c, const char *url,
                           struct playlist *pls, AVIOContext *in)
 {
@@ -944,6 +979,14 @@ static int parse_playlist(HLSContext *c, const char *url,
                     goto fail;
                 }
 
+                ret = test_segment(c->ctx, pls->ctx ? pls->ctx->iformat : NULL, pls, seg);
+                if (ret < 0) {
+                    av_free(seg->url);
+                    av_free(seg->key);
+                    av_free(seg);
+                    goto fail;
+                }
+
                 if (duration < 0.001 * AV_TIME_BASE) {
                     av_log(c->ctx, AV_LOG_WARNING, "Cannot get correct #EXTINF value of segment %s,"
                                     " set to default value to 1ms.\n", seg->url);
@@ -1981,6 +2024,11 @@ static int hls_read_header(AVFormatContext *s)
         pls->ctx->max_analyze_duration = s->max_analyze_duration > 0 ? s->max_analyze_duration : 4 * AV_TIME_BASE;
         url = av_strdup(pls->segments[0]->url);
         ret = av_probe_input_buffer(&pls->pb, &in_fmt, url, NULL, 0, 0);
+
+        for (int n = 0; n < pls->n_segments; n++)
+            if (ret >= 0)
+                ret = test_segment(s, in_fmt, pls, pls->segments[n]);
+
         av_free(url);
         if (ret < 0) {
             /* Free the ctx - it isn't initialized properly at this point,
@@ -2376,6 +2424,8 @@ static const AVOption hls_options[] = {
         OFFSET(allowed_extensions), AV_OPT_TYPE_STRING,
         {.str = "3gp,aac,avi,flac,mkv,m3u8,m4a,m4s,m4v,mpg,mov,mp2,mp3,mp4,mpeg,mpegts,ogg,ogv,oga,ts,vob,wav"},
         INT_MIN, INT_MAX, FLAGS},
+    {"extension_picky", "Be picky with all extensions matching",
+        OFFSET(extension_picky), AV_OPT_TYPE_BOOL, {.i64 = 1}, 0, 1, FLAGS},
     {"max_reload", "Maximum number of times a insufficient list is attempted to be reloaded",
         OFFSET(max_reload), AV_OPT_TYPE_INT, {.i64 = 3}, 0, INT_MAX, FLAGS},
     {"m3u8_hold_counters", "The maximum number of times to load m3u8 when it refreshes without new segments",