scsi: sg: allocate with __GFP_ZERO in sg_build_indirect()

BugLink: https://bugs.launchpad.net/bugs/1775477

commit a45b599a upstream.

This shall help avoid copying uninitialized memory to the userspace when
calling ioctl(fd, SG_IO) with an empty command.

Reported-by: syzbot+7d26fc1eea198488deab@syzkaller.appspotmail.com
Cc: stable@vger.kernel.org
Signed-off-by: Alexander Potapenko <glider@google.com>
Acked-by: Douglas Gilbert <dgilbert@interlog.com>
Reviewed-by: Johannes Thumshirn <jthumshirn@suse.de>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Stefan Bader <stefan.bader@canonical.com>
Acked-by: Kleber Sacilotto de Souza <kleber.souza@canonical.com>
Signed-off-by: Khalid Elmously <khalid.elmously@canonical.com>

drivers/scsi/sg.c

@@ -1903,7 +1903,7 @@ sg_build_indirect(Sg_scatter_hold * schp, Sg_fd * sfp, int buff_size)
 		num = (rem_sz > scatter_elem_sz_prev) ?
 			scatter_elem_sz_prev : rem_sz;
 
-		schp->pages[k] = alloc_pages(gfp_mask, order);
+		schp->pages[k] = alloc_pages(gfp_mask | __GFP_ZERO, order);
 		if (!schp->pages[k])
 			goto out;