[Bug 1837094] Re: UndefinedBehaviorSanitizer crash around slirp::ip_reass()

[Philippe Mathieu-Daudé]

I apologize for not understanding this bug was a security issue, and not
insisting on it.

It has been fixed in SLiRP by "Fix use-afte-free in ip_reass() (CVE-2020-1983)":
https://gitlab.freedesktop.org/slirp/libslirp/commit/9bd6c591

And in QEMU by commit 7769c23774 "slirp: update to fix CVE-2020-1983".

** CVE added: https://cve.mitre.org/cgi-bin/cvename.cgi?name=2020-1983

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https://bugs.launchpad.net/bugs/1837094

Title:
  UndefinedBehaviorSanitizer crash around slirp::ip_reass()

Status in QEMU:
  Fix Released

Bug description:
  tag: v4.1.0-rc1

  ./configure --enable-sanitizers --extra-cflags=-O1

  ==26130==ERROR: UndefinedBehaviorSanitizer: SEGV on unknown address 
0x000000000008 (pc 0x0000561ad346d588 bp 0x7fff6ee9f940 sp 0x7fff6ee9f8e8 
T26130)
  ==26130==The signal is caused by a WRITE memory access.
  ==26130==Hint: address points to the zero page.
      #0 0x0000561ad346d587 in ip_deq() at slirp/src/ip_input.c:411:55
      #1 0x0000561ad346cffb in ip_reass() at slirp/src/ip_input.c:304:9
      #2 0x0000561ad346cb6f in ip_input() at slirp/src/ip_input.c:184:18

  I only had access to the last packet which isn't the culprit, I'm now
  seeing how to log the network traffic of the guest to provide more
  useful information.

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