H3 SETTINGS emission has recently been delayed. The idea is to send it
with the first STREAM to reduce sendto syscall invocation. This was
implemented in the following patch :
3dd79d378c86b3ebf60e029f518add5f1ed54815
MINOR: h3: Send the h3 settings with others streams (requests)
This patch works fine under nominal conditions. However, it will cause a
crash if a HTTP/3 connection is released before having sent any data,
for example when receiving an invalid first request. In this case,
qc_release will first free qcc.app_ops HTTP/3 application protocol layer
via release callback. Then qc_send is called to emit any closing frames
built by app_ops release invocation. However, in qc_send, as no data has
been sent, it will try to complete application layer protocol
intialization, with a SETTINGS emission for HTTP/3. Thus, qcc.app_ops is
reused, which is invalid as it has been just freed. This will cause a
crash with h3_finalize in the call stack.
This bug can be reproduced artificially by generating incomplete HTTP/3
requests. This will in time trigger http-request timeout without any
data send. This is done by editing qc_handle_strm_frm function.
- ret = qcc_recv(qc->qcc, strm_frm->id, strm_frm->len,
+ ret = qcc_recv(qc->qcc, strm_frm->id, strm_frm->len - 1,
strm_frm->offset.key, strm_frm->fin,
(char *)strm_frm->data);
To fix this, application layer closing API has been adjusted to be done
in two-steps. A new shutdown callback is implemented : it is used by the
HTTP/3 layer to generate GOAWAY frame in qc_release prologue.
Application layer context qcc.app_ops is then freed later in qc_release
via the release operation which is now only used to liberate app layer
ressources. This fixes the problem as the intermediary qc_send
invocation will be able to reuse app_ops before it is freed.
This patch fixes the crash, but it would be better to adjust H3 SETTINGS
emission in case of early connection closing : in this case, there is no
need to send it. This should be implemented in a future patch.
This should fix the crash recently experienced by Tristan in github
issue #1801.
This must be backported up to 2.6.
f8aaf8bdfa