BUG/MEDIUM: quic: Possible crash during retransmissions and heavy load

BUG/MEDIUM: quic: Possible crash during retransmissions and heavy load

This bug could be reproduced with -dMfail and dectected by libasan as follows:

$ ASAN_OPTIONS=disable_coredump=0:unmap_shadow_on_exit=1:abort_on_error=f quic-freeze.cfg -dMfail -dMno-cache -dM0x55
=================================================================
==82989==ERROR: AddressSanitizer: stack-use-after-scope on address 0x7ffc 0x560790cc4749 bp 0x7fff8e0e8e30 sp 0x7fff8e0e8e28
WRITE of size 8 at 0x7fff8e0ea338 thread T0
    #0 0x560790cc4748 in qc_frm_free src/quic_frame.c:1222
    #1 0x560790cc5260 in qc_release_frm src/quic_frame.c:1261
    #2 0x560790d1de99 in qc_treat_acked_tx_frm src/quic_rx.c:312
    #3 0x560790d1e708 in qc_ackrng_pkts src/quic_rx.c:370
    #4 0x560790d22a1d in qc_parse_ack_frm src/quic_rx.c:694
    #5 0x560790d25daa in qc_parse_pkt_frms src/quic_rx.c:988
    #6 0x560790d2a509 in qc_treat_rx_pkts src/quic_rx.c:1373
    #7 0x560790c72d45 in quic_conn_io_cb src/quic_conn.c:906
    #8 0x560791207847 in run_tasks_from_lists src/task.c:596
    #9 0x5607912095f0 in process_runnable_tasks src/task.c:876
    #10 0x560791135564 in run_poll_loop src/haproxy.c:2966
    #11 0x5607911363af in run_thread_poll_loop src/haproxy.c:3165
    #12 0x56079113938c in main src/haproxy.c:3862
    #13 0x7f92606edd09 in __libc_start_main ../csu/libc-start.c:308
    #14 0x560790bcd529 in _start (/home/flecaille/src/haproxy/haproxy+0x

Address 0x7fff8e0ea338 is located in stack of thread T0 at offset 1032 i
    #0 0x560790d29b52 in qc_treat_rx_pkts src/quic_rx.c:1341

  This frame has 2 object(s):
    [32, 48) 'ar' (line 1380)
    [64, 1088) '_msg' (line 1368) <== Memory access at offset 1032 is inable
HINT: this may be a false positive if your program uses some custom stacnism, swapcontext or vfork
      (longjmp and C++ exceptions *are* supported)
SUMMARY: AddressSanitizer: stack-use-after-scope src/quic_frame.c:1222 i
Shadow bytes around the buggy address:
  0x100071c15410: f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8
  0x100071c15420: f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8
  0x100071c15430: f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8
  0x100071c15440: f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8
  0x100071c15450: f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8
=>0x100071c15460: f8 f8 f8 f8 f8 f8 f8[f8]f8 f8 f8 f8 f8 f8 f3 f3
  0x100071c15470: f3 f3 f3 f3 f3 f3 f3 f3 f3 f3 f3 f3 f3 f3 00 00
  0x100071c15480: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
  0x100071c15490: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
  0x100071c154a0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
  0x100071c154b0: 00 00 00 00 00 00 00 00 f1 f1 f1 f1 04 f3 f3 f3
Shadow byte legend (one shadow byte represents 8 application bytes):
  Addressable:           00
  Partially addressable: 01 02 03 04 05 06 07
  Heap left redzone:       fa
  Freed heap region:       fd
  Stack left redzone:      f1
  Stack mid redzone:       f2
  Stack right redzone:     f3
  Stack after return:      f5
  Stack use after scope:   f8
  Global redzone:          f9
  Global init order:       f6
  Poisoned by user:        f7
  Container overflow:      fc
  Array cookie:            ac
  Intra object redzone:    bb
  ASan internal:           fe
  Left alloca redzone:     ca
  Right alloca redzone:    cb
  Shadow gap:              cc
==82989==ABORTING
AddressSanitizer:DEADLYSIGNAL
AddressSanitizer:DEADLYSIGNAL
AddressSanitizer:DEADLYSIGNAL
AddressSanitizer:DEADLYSIGNAL
AddressSanitizer:DEADLYSIGNAL
AddressSanitizer:DEADLYSIGNAL
Aborted (core dumped)

Note that a coredump could not always be produced with all compilers. This was
always the case with clang 11.

When allocating frames to be retransmitted from qc_dgrams_retransmit(), if they
could not be sent for any reason, they could remain attached to a local list to
qc_dgrams_retransmit() and trigger a crash with libasan when releasing the
original frames they were duplicated from.

To fix this, always release the frames which could not be sent during
retransmissions calling qc_free_frm_list() where needed.

Must be backported as far as 2.6.