Re: [PATCH] util/vfio-helpers: Use g_file_read_link()

["Cédric Le Goater" <clg@redhat.com>]

Hello Akihiko,

On 5/22/23 13:49, Akihiko Odaki wrote:
> When _FORTIFY_SOURCE=2, glibc version is 2.35, and GCC version is
> 12.1.0, the compiler complains as follows:
> 
> In file included from /usr/include/features.h:490,
>                   from /usr/include/bits/libc-header-start.h:33,
>                   from /usr/include/stdint.h:26,
>                   from /usr/lib/gcc/aarch64-unknown-linux-gnu/12.1.0/include/stdint.h:9,
>                   from /home/alarm/q/var/qemu/include/qemu/osdep.h:94,
>                   from ../util/vfio-helpers.c:13:
> In function 'readlink',
>      inlined from 'sysfs_find_group_file' at ../util/vfio-helpers.c:116:9,
>      inlined from 'qemu_vfio_init_pci' at ../util/vfio-helpers.c:326:18,
>      inlined from 'qemu_vfio_open_pci' at ../util/vfio-helpers.c:517:9:
> /usr/include/bits/unistd.h:119:10: error: argument 2 is null but the corresponding size argument 3 value is 4095 [-Werror=nonnull]
>    119 |   return __glibc_fortify (readlink, __len, sizeof (char),
>        |          ^~~~~~~~~~~~~~~
> 
> This error implies the allocated buffer can be NULL. Use
> g_file_read_link(), which allocates buffer automatically to avoid the
> error.
> 
> Signed-off-by: Akihiko Odaki <akihiko.odaki@daynix.com>

There are a few other VFIO routines computing the IOMMU group from sysfs :

   vfio_ap_get_group()
   vfio_ccw_get_group()
   vfio_realize()

May be there is a possible common routine to introduce. Anyhow, this is
beyond the scope of this fix

Reviewed-by: Cédric Le Goater <clg@redhat.com>

Thanks,

C.

> ---
>   util/vfio-helpers.c | 8 +++++---
>   1 file changed, 5 insertions(+), 3 deletions(-)
> 
> diff --git a/util/vfio-helpers.c b/util/vfio-helpers.c
> index 2d8af38f88..e482ab22e2 100644
> --- a/util/vfio-helpers.c
> +++ b/util/vfio-helpers.c
> @@ -106,15 +106,17 @@ struct QEMUVFIOState {
>    */
>   static char *sysfs_find_group_file(const char *device, Error **errp)
>   {
> +    g_autoptr(GError) gerr;
>       char *sysfs_link;
>       char *sysfs_group;
>       char *p;
>       char *path = NULL;
>   
>       sysfs_link = g_strdup_printf("/sys/bus/pci/devices/%s/iommu_group", device);
> -    sysfs_group = g_malloc0(PATH_MAX);
> -    if (readlink(sysfs_link, sysfs_group, PATH_MAX - 1) == -1) {
> -        error_setg_errno(errp, errno, "Failed to find iommu group sysfs path");
> +    sysfs_group = g_file_read_link(sysfs_link, &gerr);
> +    if (gerr) {
> +        error_setg(errp, "Failed to find iommu group sysfs path: %s",
> +                   gerr->message);
>           goto out;
>       }
>       p = strrchr(sysfs_group, '/');