linux-kernel - Re: fs/proc/task_mmu.c:598:48: error: cast to pointer from integer of different size

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Message-Id: <5f1f44be-80ad-4b4e-90a0-c2e4e8cd3dbf@app.fastmail.com>
Date: Mon, 01 Jul 2024 13:58:05 +0200
From: "Arnd Bergmann" <arnd@...db.de>
To: "Naresh Kamboju" <naresh.kamboju@...aro.org>,
 "open list" <linux-kernel@...r.kernel.org>, linux-fsdevel@...r.kernel.org,
 lkft-triage@...ts.linaro.org
Cc: "Jan Kara" <jack@...e.cz>, "Christian Brauner" <brauner@...nel.org>,
 "Hugh Dickins" <hughd@...gle.com>, "Andrii Nakryiko" <andrii@...nel.org>,
 "Alexander Viro" <viro@...iv.linux.org.uk>,
 "Dan Carpenter" <dan.carpenter@...aro.org>,
 "Anders Roxell" <anders.roxell@...aro.org>
Subject: Re: fs/proc/task_mmu.c:598:48: error: cast to pointer from integer of
 different size

On Mon, Jul 1, 2024, at 12:19, Naresh Kamboju wrote:
> fs/proc/task_mmu.c: In function 'do_procmap_query':
> fs/proc/task_mmu.c:598:48: error: cast to pointer from integer of
> different size [-Werror=int-to-pointer-cast]
>   598 |         if (karg.vma_name_size && copy_to_user((void __user
> *)karg.vma_name_addr,
>       |                                                ^
> fs/proc/task_mmu.c:605:48: error: cast to pointer from integer of
> different size [-Werror=int-to-pointer-cast]
>   605 |         if (karg.build_id_size && copy_to_user((void __user
> *)karg.build_id_addr,
>       |                                                ^
> cc1: all warnings being treated as errors
>

There is already a fix in linux-next:

@@ -595,14 +595,14 @@ static int do_procmap_query(struct proc_maps_private *priv, void __user *uarg)
        query_vma_teardown(mm, vma);
        mmput(mm);
 
-       if (karg.vma_name_size && copy_to_user((void __user *)karg.vma_name_addr,
+       if (karg.vma_name_size && copy_to_user((void __user *)(uintptr_t)karg.vma_name_addr,
                                               name, karg.vma_name_size)) {
                kfree(name_buf);
                return -EFAULT;
        }


This could be expressed slightly nicer using u64_to_user_ptr(),
but functionally that is the same.

I also see a slight issue in the use of .compat_ioctl:

 const struct file_operations proc_pid_maps_operations = {
        .open           = pid_maps_open,
        .read           = seq_read,
        .llseek         = seq_lseek,
        .release        = proc_map_release,
+       .unlocked_ioctl = procfs_procmap_ioctl,
+       .compat_ioctl   = procfs_procmap_ioctl,
 };
 

Since the argument is always a pointer, this should be

       .compat_ioctl = compat_ptr_ioctl,

In practice this is only relevant on 32-bit s390
tasks to sanitize the pointer value.

     Arnd