On 23/02/2022 15.36, wli...@stu.xidian.edu.cn wrote:
Hi all,
I find a potential Use-after-free in QEMU 6.2.0, which is in
virtio_iommu_handle_command() (./hw/virtio/virtio-iommu.c).
Specifically, in the loop body, the variable 'buf' allocated at line 639 can
be freed by g_free() at line 659. However, if the execution path enters the
loop body again and the if branch takes true at line 616, the control will
directly jump to 'out' at line 651. At this time, 'buf' is a freed pointer,
which is not assigned with an allocated memory but used at line 653. As a
result, a UAF bug is triggered.
599 for (;;) {
...
615 sz = iov_to_buf(iov, iov_cnt, 0, &head, sizeof(head));
616 if (unlikely(sz != sizeof(head))) {
617 tail.status = VIRTIO_IOMMU_S_DEVERR;
618 goto out;
619 }
...
639 buf = g_malloc0(output_size);
...
651out:
652 sz = iov_from_buf(elem->in_sg, elem->in_num, 0,
653 buf ? buf : &tail, output_size);
...
659 g_free(buf);
660 }
We can fix it by set ‘buf‘ to NULL after freeing it:
651out:
652 sz = iov_from_buf(elem->in_sg, elem->in_num, 0,
653 buf ? buf : &tail, output_size);
...
659 g_free(buf);
+++buf = NULL;
660 }
I'm looking forward to your confirmation.
Hi,
thanks for your report and patch - but to make sure that the right people
get attention, please use the scripts/get_maintainer.pl script to get a list
of people who should be on CC:, or look into the MAINTAINERS file directly
(for the next time - this time, I've CC:ed them now already).
Thanks,
Thomas
