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async: avoid use-after-free on re-entrancy guard 

A BH callback can free the BH, causing a use-after-free in aio_bh_call.
Fix that by keeping a local copy of the re-entrancy guard pointer.

Buglink: https://bugs.chromium.org/p/oss-fuzz/issues/detail?id=58513
Fixes: 9c86c97f12 ("async: Add an optional reentrancy guard to the BH API")
Signed-off-by: Alexander Bulekov <alxndr@bu.edu>
Message-Id: <20230501141956.3444868-1-alxndr@bu.edu>
Reviewed-by: Thomas Huth <thuth@redhat.com>
Signed-off-by: Thomas Huth <thuth@redhat.com>
master
Alexander Bulekov 2023-05-01 10:19:56 -04:00 committed by Thomas Huth
parent b08dc0f1b7
commit 7915bd06f2
1 changed files with 8 additions and 6 deletions
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14
util/async.c
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@ -156,18 +156,20 @@ void aio_bh_call(QEMUBH *bh)
{
bool last_engaged_in_io = false;
if (bh->reentrancy_guard) {
last_engaged_in_io = bh->reentrancy_guard->engaged_in_io;
if (bh->reentrancy_guard->engaged_in_io) {
/* Make a copy of the guard-pointer as cb may free the bh */
MemReentrancyGuard *reentrancy_guard = bh->reentrancy_guard;
if (reentrancy_guard) {
last_engaged_in_io = reentrancy_guard->engaged_in_io;
if (reentrancy_guard->engaged_in_io) {
trace_reentrant_aio(bh->ctx, bh->name);
}
bh->reentrancy_guard->engaged_in_io = true;
reentrancy_guard->engaged_in_io = true;
}
bh->cb(bh->opaque);
if (bh->reentrancy_guard) {
bh->reentrancy_guard->engaged_in_io = last_engaged_in_io;
if (reentrancy_guard) {
reentrancy_guard->engaged_in_io = last_engaged_in_io;
}
}