Copied from <https://chromium.googlesource.com/webm/libvpx/+/1c758781c428c0e895645b95b8ff1512b6bdcecb%5E%21/>
See also: <https://www.mozilla.org/en-US/security/advisories/mfsa2025-44/#CVE-2025-5262>
     and: <https://hg-edge.mozilla.org/releases/mozilla-esr128/rev/69f53ce5ef0bca2816a3b13cae570e835938c010>

Author: James Zern <jzern@google.com>	Thu May 01 02:28:48 2025

vpx_codec_enc_init_multi: fix double free on init failure

In `vp8e_init()`, the encoder would take ownership of
`mr_cfg.mr_low_res_mode_info` even if `vp8_create_compressor()` failed.
This caused confusion at the call site as other failures in
`vp8e_init()` did not result in ownership transfer and the caller would
free the memory. In the case of `vp8_create_compressor()` failure both
the caller and `vpx_codec_destroy()` would free the memory, causing a
crash. `mr_*` related variables are now cleared on failure to prevent
this situation.

Bug: webm:413411335
Bug: https://bugzilla.mozilla.org/show_bug.cgi?id=1962421
Change-Id: Ie951d42b9029a586bf9059b650bd8863db9f9ffc

--- a/vp8/vp8_cx_iface.c
+++ b/vp8/vp8_cx_iface.c
@@ -727,17 +727,27 @@ static vpx_codec_err_t vp8e_init(vpx_cod
       priv->pts_offset_initialized = 0;
       priv->timestamp_ratio.den = priv->cfg.g_timebase.den;
       priv->timestamp_ratio.num = (int64_t)priv->cfg.g_timebase.num;
       priv->timestamp_ratio.num *= TICKS_PER_SEC;
       reduce_ratio(&priv->timestamp_ratio);
 
       set_vp8e_config(&priv->oxcf, priv->cfg, priv->vp8_cfg, mr_cfg);
       priv->cpi = vp8_create_compressor(&priv->oxcf);
-      if (!priv->cpi) res = VPX_CODEC_MEM_ERROR;
+      if (!priv->cpi) {
+#if CONFIG_MULTI_RES_ENCODING
+        // Release ownership of mr_cfg->mr_low_res_mode_info on failure. This
+        // prevents ownership confusion with the caller and avoids a double
+        // free when vpx_codec_destroy() is called on this instance.
+        priv->oxcf.mr_total_resolutions = 0;
+        priv->oxcf.mr_encoder_id = 0;
+        priv->oxcf.mr_low_res_mode_info = NULL;
+#endif
+        res = VPX_CODEC_MEM_ERROR;
+      }
     }
   }
 
   return res;
 }
 
 static vpx_codec_err_t vp8e_destroy(vpx_codec_alg_priv_t *ctx) {
 #if CONFIG_MULTI_RES_ENCODING
--- a/vpx/src/vpx_encoder.c
+++ b/vpx/src/vpx_encoder.c
@@ -109,16 +109,19 @@ vpx_codec_err_t vpx_codec_enc_init_multi
           mr_cfg.mr_down_sampling_factor.num = dsf->num;
           mr_cfg.mr_down_sampling_factor.den = dsf->den;
 
           ctx->iface = iface;
           ctx->name = iface->name;
           ctx->priv = NULL;
           ctx->init_flags = flags;
           ctx->config.enc = cfg;
+          // ctx takes ownership of mr_cfg.mr_low_res_mode_info if and only if
+          // this call succeeds. The first ctx entry in the array is
+          // responsible for freeing the memory.
           res = ctx->iface->init(ctx, &mr_cfg);
         }
 
         if (res) {
           const char *error_detail = ctx->priv ? ctx->priv->err_detail : NULL;
           /* Destroy current ctx */
           ctx->err_detail = error_detail;
           vpx_codec_destroy(ctx);