From: Alexander Bulekov <alx...@bu.edu> 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 <alx...@bu.edu> Message-Id: <20230501141956.3444868-1-alx...@bu.edu> Reviewed-by: Thomas Huth <th...@redhat.com> Signed-off-by: Thomas Huth <th...@redhat.com> --- util/async.c | 14 ++++++++------ 1 file changed, 8 insertions(+), 6 deletions(-) diff --git a/util/async.c b/util/async.c index 9df7674b4e..055070ffbd 100644 --- a/util/async.c +++ b/util/async.c @@ -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; } } -- 2.31.1
