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Re: [libvirt] [PATCH] qemu: avoid text monitor null deref



On Wed, Oct 12, 2011 at 06:21:37PM -0600, Eric Blake wrote:
> Detected by Coverity.  If, for some reason, our text monitor input
> does not match our assumptions, we end up incrementing p while it
> is NULL, then dereferencing the pointer 0x1, which will fault.
> 
> * src/qemu/qemu_monitor_text.c
> (qemuMonitorTextGetBlockStatsParamsNumber): Rewrite to avoid
> deref of strchr failure.  Fix indentation.
> ---
>  src/qemu/qemu_monitor_text.c |   33 +++++++++++++++------------------
>  1 files changed, 15 insertions(+), 18 deletions(-)
> 
> diff --git a/src/qemu/qemu_monitor_text.c b/src/qemu/qemu_monitor_text.c
> index 51e8c5c..1eb9846 100644
> --- a/src/qemu/qemu_monitor_text.c
> +++ b/src/qemu/qemu_monitor_text.c
> @@ -1036,26 +1036,23 @@ int qemuMonitorTextGetBlockStatsParamsNumber(qemuMonitorPtr mon,
>       * "floppy0: ")
>       */
>      p = strchr(p, ' ');
> -    p++;

  okay, clearly that's dangerous

> -    while (*p) {
> -            if (STRPREFIX (p, "rd_bytes=") ||
> -                STRPREFIX (p, "wr_bytes=") ||
> -                STRPREFIX (p, "rd_operations=") ||
> -                STRPREFIX (p, "wr_operations=") ||
> -                STRPREFIX (p, "rd_total_times_ns=") ||
> -                STRPREFIX (p, "wr_total_times_ns=") ||
> -                STRPREFIX (p, "flush_operations=") ||
> -                STRPREFIX (p, "flush_total_times_ns=")) {
> -                num++;
> -            } else {
> -                VIR_DEBUG ("unknown block stat near %s", p);
> -            }
> +    while (p && p < eol) {
> +        if (STRPREFIX (p, " rd_bytes=") ||
> +            STRPREFIX (p, " wr_bytes=") ||
> +            STRPREFIX (p, " rd_operations=") ||
> +            STRPREFIX (p, " wr_operations=") ||
> +            STRPREFIX (p, " rd_total_times_ns=") ||
> +            STRPREFIX (p, " wr_total_times_ns=") ||
> +            STRPREFIX (p, " flush_operations=") ||
> +            STRPREFIX (p, " flush_total_times_ns=")) {
> +            num++;
> +        } else {
> +            VIR_DEBUG ("unknown block stat near %s", p);
> +        }
> 
> -            /* Skip to next label. */
> -            p = strchr (p, ' ');
> -            if (!p || p >= eol) break;
> -            p++;
> +        /* Skip to next label. */
> +        p = strchr(p + 1, ' ');
>      }
> 
>      *nparams = num;

  ACK,

Daniel

-- 
Daniel Veillard      | libxml Gnome XML XSLT toolkit  http://xmlsoft.org/
daniel veillard com  | Rpmfind RPM search engine http://rpmfind.net/
http://veillard.com/ | virtualization library  http://libvirt.org/


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