Re: [PATCH] qga: Fix ubsan warning

["Daniel P. Berrangé" <berrange@redhat.com>]

On Mon, Jul 28, 2025 at 07:30:16PM +0200, Thomas Huth wrote:
> From: Thomas Huth <thuth@redhat.com>
> 
> When compiling QEMU with --enable-ubsan there is a undefined behavior
> warning when running "make check":
> 
>  .../qga/commands-linux.c:452:15: runtime error: applying non-zero offset 5 to null pointer
>  #0 0x55ea7b89450c in build_guest_fsinfo_for_pci_dev ..../qga/commands-linux.c:452:15
> 
> Add a check to avoid incrementing the NULL pointer here.
> 
> Signed-off-by: Thomas Huth <thuth@redhat.com>
> ---
>  qga/commands-linux.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/qga/commands-linux.c b/qga/commands-linux.c
> index 9e8a934b9a6..caf7c3ca22b 100644
> --- a/qga/commands-linux.c
> +++ b/qga/commands-linux.c
> @@ -449,7 +449,9 @@ static bool build_guest_fsinfo_for_pci_dev(char const *syspath,
>          has_ata = true;
>      } else {
>          p = strstr(syspath, "/host");
> -        q = p + 5;
> +        if (p) {
> +            q = p + 5;
> +        }
>      }
>      if (p && sscanf(q, "%u", &host) == 1) {

q is always non-NULL if p is non-NULL, so this is safe, but I would be more
happy with this changing to 'q && sscanf' to eliminate the indirection.


With regards,
Daniel
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