BUG/MEDIUM: mux-h2: make sure not to touch dummy streams when sending WU

Since commit 1cc851d9f2 ("MEDIUM: mux-h2: start to update stream when
sending WU") we started storing stream offsets in the h2s struct. These
offsets are updated at a few points, where it's safe to write to the
stream, and in h2c_send_strm_wu(), where the h2s->h2c was not performed.

Due to this, nothing protects the h2s from being updated when sending a
WU for a closed stream, which might only happen when acknowledging a
frame after resetting that stream, which is quite unlikely. In any case
if this happens, it will crash as in issue #2793 since the closed streams
are purposely read-only to catch such bugs.

The fix is trivial, just check h2s->h2c before deciding to update the
stream.

Thanks to @Wahnes for reporting this, and Christopher for spotting the
cause. This needs to be backported to 3.1 only.

diff --git a/src/mux_h2.c b/src/mux_h2.c
index 970223c42b30ac280a310cb3c2cf340a085e12da..9788753f6b57e48e010892e807e89a33963f1652 100644 (file)
--- a/src/mux_h2.c
+++ b/src/mux_h2.c
@@ -2991,7 +2991,7 @@ static int h2c_send_strm_wu(struct h2c *h2c)
        if (ret > 0) {
                h2c->wu_s = 0;
                h2s = h2c_st_by_id(h2c, h2c->dsi);
-               if (h2s)
+               if (h2s && h2s->h2c)
                        h2s->last_adv_ofs = h2s->next_max_ofs;
        }
  out: