Re: [PATCH v3 3/3] qga-win: prevent crash when executing guest-file-read with large count

["Philippe Mathieu-Daudé" <philmd@redhat.com>]

On 3/11/20 6:04 PM, Basil Salman wrote:
> BZ: #1594054

^ This is not very helpful as it... (think to ppl with no knowledge of 
'BZ', what to do with this number). Instead ...

> guest-file-read command is currently implemented to read from a
> file handle count number of bytes. when executed with a very large count number
> qemu-ga crashes.
> after some digging turns out that qemu-ga crashes after trying to allocate
> a buffer large enough to save the data read in it, the buffer was allocated using
> g_malloc0 which is not fail safe, and results a crash in case of failure.
> g_malloc0 was replaced with g_try_malloc0() which returns NULL on failure,
> A check was added for that case in order to prevent qemu-ga from crashing
> and to send a response to the qemu-ga client accordingly.
> 

... add here (see 
https://wiki.qemu.org/Contribute/SubmitAPatch#Write_a_meaningful_commit_message):

Buglink: https://bugzilla.redhat.com/show_bug.cgi?id=1594054

Also add:

Cc: qemu-stable@nongnu.org

> Signed-off-by: Basil Salman <basil@daynix.com>
> ---
>   qga/commands-win32.c | 8 +++++++-
>   1 file changed, 7 insertions(+), 1 deletion(-)
> 
> diff --git a/qga/commands-win32.c b/qga/commands-win32.c
> index 9c744d6405..b49920e201 100644
> --- a/qga/commands-win32.c
> +++ b/qga/commands-win32.c
> @@ -343,7 +343,13 @@ GuestFileRead *qmp_guest_file_read(int64_t handle, bool has_count,
>       }
>   
>       fh = gfh->fh;
> -    buf = g_malloc0(count+1);
> +    buf = g_try_malloc0(count + 1);
> +    if (!buf) {
> +        error_setg(errp,
> +                   "failed to allocate sufficient memory "
> +                   "to complete the requested service");
> +        return NULL;
> +    }

Can you fix the equivalent problem in qga/commands-posix.c too please?

Also use "PATCH-for-5.0" in the patch subject so we don't miss it for 
the next release.

Thanks!

Phil.

>       is_ok = ReadFile(fh, buf, count, &read_count, NULL);
>       if (!is_ok) {
>           error_setg_win32(errp, GetLastError(), "failed to read file");
>