[0/6] 9pfs: fix fstat() after unlink() (with a Linux guest)

Message

Christian Schoenebeck Nov. 24, 2024, 4:28 p.m. UTC

This fixes an infamous, long standing bug:
https://gitlab.com/qemu-project/qemu/-/issues/103

* Actual fix of this bug is patch 5.

* Patches 1 and 6 add a test case to verify the expected behaviour.

* The other patches (2, 3, 4) are basically just minor cleanup patches more
  or less (un)related that I simply did not bother to send separately.

Probably there are still other 9p request types that should be fixed for this
use-after-unlink idiom, but this series fixes the mentioned bug report as
described by reporter, so fair enough to round this up here for now.

Simple test app to verify this behaviour on a Linux guest:

#include <stdio.h>
#include <stdlib.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <unistd.h>
#include <fcntl.h>

int main() {
  struct stat st;
  int fd = open("doa-file", O_RDWR | O_CREAT | O_EXCL, 0600);
  unlink("doa-file");
  int res = fstat(fd, &st);
  printf("fstat() = %d\n", res);
  return res;
}

Christian Schoenebeck (6):
  tests/9p: add 'use-after-unlink' test
  tests/9p: fix Rreaddir response name
  tests/9p: add missing Rgetattr response name
  9pfs: remove obsolete comment in v9fs_getattr()
  9pfs: fix 'Tgetattr' after unlink
  tests/9p: also check 'Tgetattr' in 'use-after-unlink' test

 hw/9pfs/9p.c                          | 12 ++++---
 tests/qtest/libqos/virtio-9p-client.c |  3 +-
 tests/qtest/virtio-9p-test.c          | 46 +++++++++++++++++++++++++++
 3 files changed, 55 insertions(+), 6 deletions(-)