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Date:   Thu, 5 Apr 2018 20:56:50 +0200
From:   Michal Hocko <mhocko@kernel.org>
To:     Cyrill Gorcunov <gorcunov@gmail.com>
Cc:     LKML <linux-kernel@vger.kernel.org>,
        Randy Dunlap <rdunlap@infradead.org>,
        Andrey Vagin <avagin@openvz.org>,
        Andrew Morton <akpm@linuxfoundation.org>,
        Pavel Emelyanov <xemul@virtuozzo.com>,
        Michael Kerrisk <mtk.manpages@gmail.com>,
        Yang Shi <yang.shi@linux.alibaba.com>
Subject: Re: [PATCH v2] prctl: Deprecate non PR_SET_MM_MAP operations
Message-ID: <20180405185650.GR6312@dhcp22.suse.cz>
References: <20180405182651.GM15783@uranus.lan>
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On Thu 05-04-18 21:26:51, Cyrill Gorcunov wrote:
> An ability to manipulate mm_struct fields was introduced in
> sake of CRIU in first place. Later we provide more suitable
> and safe operation PR_SET_MM_MAP where all fields to be modifed
> are passed in one structure which allows us to make more detailed
> verification.

I hope this will serve as a memento for future single-user APIs
proposals. The whole thing was a bad idea since the beginning.

> Still old interface remains present for compatibility reason
> though CRIU itself already switched to PR_SET_MM_MAP on its
> own long ago.
> 
> Googling didn't reveal some other users of this operation
> so I think it should be safe to remove this interface.
> 
> v2:
>  - Improve warning message
>  - Drop redundant args check
> 
> CC: Andrey Vagin <avagin@openvz.org>
> CC: Andrew Morton <akpm@linuxfoundation.org>
> CC: Pavel Emelyanov <xemul@virtuozzo.com>
> CC: Michael Kerrisk <mtk.manpages@gmail.com>
> CC: Yang Shi <yang.shi@linux.alibaba.com>
> CC: Michal Hocko <mhocko@kernel.org>
> Signed-off-by: Cyrill Gorcunov <gorcunov@gmail.com>

Acked-by: Michal Hocko <mhocko@suse.com>

and fingers crossed that we haven't grown other users outside of CRIU
which is quite bound to specific kernels AFAIK.

> ---
>  kernel/sys.c |  151 -----------------------------------------------------------
>  1 file changed, 2 insertions(+), 149 deletions(-)
> 
> Index: linux-ml.git/kernel/sys.c
> ===================================================================
> --- linux-ml.git.orig/kernel/sys.c
> +++ linux-ml.git/kernel/sys.c
> @@ -2053,163 +2053,16 @@ static int prctl_set_mm_map(int opt, con
>  }
>  #endif /* CONFIG_CHECKPOINT_RESTORE */
>  
> -static int prctl_set_auxv(struct mm_struct *mm, unsigned long addr,
> -			  unsigned long len)
> -{
> -	/*
> -	 * This doesn't move the auxiliary vector itself since it's pinned to
> -	 * mm_struct, but it permits filling the vector with new values.  It's
> -	 * up to the caller to provide sane values here, otherwise userspace
> -	 * tools which use this vector might be unhappy.
> -	 */
> -	unsigned long user_auxv[AT_VECTOR_SIZE];
> -
> -	if (len > sizeof(user_auxv))
> -		return -EINVAL;
> -
> -	if (copy_from_user(user_auxv, (const void __user *)addr, len))
> -		return -EFAULT;
> -
> -	/* Make sure the last entry is always AT_NULL */
> -	user_auxv[AT_VECTOR_SIZE - 2] = 0;
> -	user_auxv[AT_VECTOR_SIZE - 1] = 0;
> -
> -	BUILD_BUG_ON(sizeof(user_auxv) != sizeof(mm->saved_auxv));
> -
> -	task_lock(current);
> -	memcpy(mm->saved_auxv, user_auxv, len);
> -	task_unlock(current);
> -
> -	return 0;
> -}
> -
>  static int prctl_set_mm(int opt, unsigned long addr,
>  			unsigned long arg4, unsigned long arg5)
>  {
> -	struct mm_struct *mm = current->mm;
> -	struct prctl_mm_map prctl_map;
> -	struct vm_area_struct *vma;
> -	int error;
> -
> -	if (arg5 || (arg4 && (opt != PR_SET_MM_AUXV &&
> -			      opt != PR_SET_MM_MAP &&
> -			      opt != PR_SET_MM_MAP_SIZE)))
> -		return -EINVAL;
> -
>  #ifdef CONFIG_CHECKPOINT_RESTORE
>  	if (opt == PR_SET_MM_MAP || opt == PR_SET_MM_MAP_SIZE)
>  		return prctl_set_mm_map(opt, (const void __user *)addr, arg4);
>  #endif
>  
> -	if (!capable(CAP_SYS_RESOURCE))
> -		return -EPERM;
> -
> -	if (opt == PR_SET_MM_EXE_FILE)
> -		return prctl_set_mm_exe_file(mm, (unsigned int)addr);
> -
> -	if (opt == PR_SET_MM_AUXV)
> -		return prctl_set_auxv(mm, addr, arg4);
> -
> -	if (addr >= TASK_SIZE || addr < mmap_min_addr)
> -		return -EINVAL;
> -
> -	error = -EINVAL;
> -
> -	down_write(&mm->mmap_sem);
> -	vma = find_vma(mm, addr);
> -
> -	prctl_map.start_code	= mm->start_code;
> -	prctl_map.end_code	= mm->end_code;
> -	prctl_map.start_data	= mm->start_data;
> -	prctl_map.end_data	= mm->end_data;
> -	prctl_map.start_brk	= mm->start_brk;
> -	prctl_map.brk		= mm->brk;
> -	prctl_map.start_stack	= mm->start_stack;
> -	prctl_map.arg_start	= mm->arg_start;
> -	prctl_map.arg_end	= mm->arg_end;
> -	prctl_map.env_start	= mm->env_start;
> -	prctl_map.env_end	= mm->env_end;
> -	prctl_map.auxv		= NULL;
> -	prctl_map.auxv_size	= 0;
> -	prctl_map.exe_fd	= -1;
> -
> -	switch (opt) {
> -	case PR_SET_MM_START_CODE:
> -		prctl_map.start_code = addr;
> -		break;
> -	case PR_SET_MM_END_CODE:
> -		prctl_map.end_code = addr;
> -		break;
> -	case PR_SET_MM_START_DATA:
> -		prctl_map.start_data = addr;
> -		break;
> -	case PR_SET_MM_END_DATA:
> -		prctl_map.end_data = addr;
> -		break;
> -	case PR_SET_MM_START_STACK:
> -		prctl_map.start_stack = addr;
> -		break;
> -	case PR_SET_MM_START_BRK:
> -		prctl_map.start_brk = addr;
> -		break;
> -	case PR_SET_MM_BRK:
> -		prctl_map.brk = addr;
> -		break;
> -	case PR_SET_MM_ARG_START:
> -		prctl_map.arg_start = addr;
> -		break;
> -	case PR_SET_MM_ARG_END:
> -		prctl_map.arg_end = addr;
> -		break;
> -	case PR_SET_MM_ENV_START:
> -		prctl_map.env_start = addr;
> -		break;
> -	case PR_SET_MM_ENV_END:
> -		prctl_map.env_end = addr;
> -		break;
> -	default:
> -		goto out;
> -	}
> -
> -	error = validate_prctl_map(&prctl_map);
> -	if (error)
> -		goto out;
> -
> -	switch (opt) {
> -	/*
> -	 * If command line arguments and environment
> -	 * are placed somewhere else on stack, we can
> -	 * set them up here, ARG_START/END to setup
> -	 * command line argumets and ENV_START/END
> -	 * for environment.
> -	 */
> -	case PR_SET_MM_START_STACK:
> -	case PR_SET_MM_ARG_START:
> -	case PR_SET_MM_ARG_END:
> -	case PR_SET_MM_ENV_START:
> -	case PR_SET_MM_ENV_END:
> -		if (!vma) {
> -			error = -EFAULT;
> -			goto out;
> -		}
> -	}
> -
> -	mm->start_code	= prctl_map.start_code;
> -	mm->end_code	= prctl_map.end_code;
> -	mm->start_data	= prctl_map.start_data;
> -	mm->end_data	= prctl_map.end_data;
> -	mm->start_brk	= prctl_map.start_brk;
> -	mm->brk		= prctl_map.brk;
> -	mm->start_stack	= prctl_map.start_stack;
> -	mm->arg_start	= prctl_map.arg_start;
> -	mm->arg_end	= prctl_map.arg_end;
> -	mm->env_start	= prctl_map.env_start;
> -	mm->env_end	= prctl_map.env_end;
> -
> -	error = 0;
> -out:
> -	up_write(&mm->mmap_sem);
> -	return error;
> +	pr_warn_once("PR_SET_MM_* has been removed. Use PR_SET_MM_MAP instead\n");
> +	return -EINVAL;
>  }
>  
>  #ifdef CONFIG_CHECKPOINT_RESTORE

-- 
Michal Hocko
SUSE Labs