Re: [PATCH-for-6.2 v2 1/2] hw/nvme/ctrl: Fix buffer overrun in nvme_changed_nslist (CVE-2021-3947)

[Klaus Jensen]

On Nov 17 13:35, Philippe Mathieu-Daudé wrote:
> Both 'buf_len' and 'off' arguments are under guest control.
> Since nvme_c2h() doesn't check out of boundary access, the
> caller must check for eventual buffer overrun on 'trans_len'.
> 
> Cc: qemu-stable@nongnu.org
> Reported-by: Qiuhao Li <Qiuhao.Li@outlook.com>
> Fixes: f432fdfa121 ("support changed namespace asynchronous event")
> Signed-off-by: Philippe Mathieu-Daudé <philmd@redhat.com>
> ---
>  hw/nvme/ctrl.c | 5 ++++-
>  1 file changed, 4 insertions(+), 1 deletion(-)
> 
> diff --git a/hw/nvme/ctrl.c b/hw/nvme/ctrl.c
> index 6a571d18cfa..93a24464647 100644
> --- a/hw/nvme/ctrl.c
> +++ b/hw/nvme/ctrl.c
> @@ -4168,8 +4168,11 @@ static uint16_t nvme_changed_nslist(NvmeCtrl *n, 
> uint8_t rae, uint32_t buf_len,
>      int i = 0;
>      uint32_t nsid;
>  
> -    memset(nslist, 0x0, sizeof(nslist));
>      trans_len = MIN(sizeof(nslist) - off, buf_len);
> +    if (trans_len >= sizeof(nslist)) {
> +        return NVME_INVALID_FIELD | NVME_DNR;
> +    }
> +    memset(nslist, 0x0, sizeof(nslist));
>  
>      while ((nsid = find_first_bit(n->changed_nsids, NVME_CHANGED_NSID_SIZE)) 
> !=
>              NVME_CHANGED_NSID_SIZE) {

The issue I mentioned with off > sizeof(nslist). I'll send a fix that
just deals with it like all the other log pages.

There is probably a better way to do these checks, but I'm not sure how
right now.

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