Re: [PATCH v2] qga: Fix ubsan warning

[Kostiantyn Kostiuk <kkostiuk@redhat.com>]

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Reviewed-by: Kostiantyn Kostiuk <kkostiuk@redhat.com>

@Thomas Huth <thuth@redhat.com> Is this fix critical to merge during code
freeze?

On Wed, Jul 30, 2025 at 10:27 AM Thomas Huth <thuth@redhat.com> 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
>
> Fix it by avoiding the additional pointer variable here and use an
> "offset" integer variable instead.
>
> Signed-off-by: Thomas Huth <thuth@redhat.com>
> ---
>  v2: Use an integer offset variable instead for checking for a NULL pointer
>
>  qga/commands-linux.c | 10 +++++-----
>  1 file changed, 5 insertions(+), 5 deletions(-)
>
> diff --git a/qga/commands-linux.c b/qga/commands-linux.c
> index 9e8a934b9a6..0c41eb97190 100644
> --- a/qga/commands-linux.c
> +++ b/qga/commands-linux.c
> @@ -400,10 +400,10 @@ static bool build_guest_fsinfo_for_pci_dev(char
> const *syspath,
>                                             Error **errp)
>  {
>      unsigned int pci[4], host, hosts[8], tgt[3];
> -    int i, nhosts = 0, pcilen;
> +    int i, offset, nhosts = 0, pcilen;
>      GuestPCIAddress *pciaddr = disk->pci_controller;
>      bool has_ata = false, has_host = false, has_tgt = false;
> -    char *p, *q, *driver = NULL;
> +    char *p, *driver = NULL;
>      bool ret = false;
>
>      p = strstr(syspath, "/devices/pci");
> @@ -445,13 +445,13 @@ static bool build_guest_fsinfo_for_pci_dev(char
> const *syspath,
>
>      p = strstr(syspath, "/ata");
>      if (p) {
> -        q = p + 4;
> +        offset = 4;
>          has_ata = true;
>      } else {
>          p = strstr(syspath, "/host");
> -        q = p + 5;
> +        offset = 5;
>      }
> -    if (p && sscanf(q, "%u", &host) == 1) {
> +    if (p && sscanf(p + offset, "%u", &host) == 1) {
>          has_host = true;
>          nhosts = build_hosts(syspath, p, has_ata, hosts,
>                               ARRAY_SIZE(hosts), errp);
> --
> 2.50.1
>
>

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