qemu crashes when doing iotest on virtio-9p filesystem

[fangying]

Qemu crashes when doing avocado-vt test on virtio-9p filesystem.
This bug can be reproduced running https://github.com/autotest/tp-qemu/blob/master/qemu/tests/9p.py with the latest qemu-4.0.0.
The crash stack goes like:

Program terminated with signal SIGSEGV, Segmentation fault.
#0 v9fs_mark_fids_unreclaim (pdu=pdu@entry=0xaaab00046868, path=path@entry=0xffff851e2fa8)
    at hw/9pfs/9p.c:505
#1 0x0000aaaae3585acc in v9fs_unlinkat (opaque=0xaaab00046868) at hw/9pfs/9p.c:2590
#2 0x0000aaaae3811c10 in coroutine_trampoline (i0=<optimized out>, i1=<optimized out>)
    at util/coroutine-ucontext.c:116
#3 0x0000ffffa13ddb20 in ?? () from /lib64/libc.so.6
Backtrace stopped: not enough registers or memory available to unwind further

A segment fault is triggered at hw/9pfs/9p.c line 505

    for (fidp = s->fid_list; fidp; fidp = fidp->next) {
        if (fidp->path.size != path->size) { # fidp is invalid
            continue;
        }

(gdb) p path
$10 = (V9fsPath *) 0xffff851e2fa8
(gdb) p *path
$11 = {size = 21, data = 0xaaaafed6f420 "./9p_test/p2a1/d0/f1"}
(gdb) p *fidp
Cannot access memory at address 0x101010101010101
(gdb) p *pdu
$12 = {size = 19, tag = 54, id = 76 'L', cancelled = 0 '\000', complete = {entries = {
      sqh_first = 0x0, sqh_last = 0xaaab00046870}}, s = 0xaaab000454b8, next = {
    le_next = 0xaaab000467c0, le_prev = 0xaaab00046f88}, idx = 88}
(gdb)

Address Sanitizer shows error and saying that there is a heap-use-after-free on *fidp*.

[Thomas Huth (th-huth)]

This is an automated cleanup. This bug report has been moved to QEMU's
new bug tracker on gitlab.com and thus gets marked as 'expired' now.
Please continue with the discussion here:

 https://gitlab.com/qemu-project/qemu/-/issues/181