linux-kernel - Re: [patch 3/4] prctl: PR_SET_MM -- Factor out mmap_sem when update mm::exe

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Date:	Mon, 4 Aug 2014 22:22:07 +0200
From:	"Serge E. Hallyn" <serge@...lyn.com>
To:	Cyrill Gorcunov <gorcunov@...nvz.org>
Cc:	linux-kernel@...r.kernel.org, keescook@...omium.org, tj@...nel.org,
	akpm@...ux-foundation.org, avagin@...nvz.org,
	ebiederm@...ssion.com, hpa@...or.com, serge.hallyn@...onical.com,
	xemul@...allels.com, segoon@...nwall.com,
	kamezawa.hiroyu@...fujitsu.com, mtk.manpages@...il.com,
	jln@...gle.com
Subject: Re: [patch 3/4] prctl: PR_SET_MM -- Factor out mmap_sem when update
 mm::exe_file

Quoting Cyrill Gorcunov (gorcunov@...nvz.org):
> Instead of taking mm->mmap_sem inside prctl_set_mm_exe_file move
> it out of and rename the helper to prctl_set_mm_exe_file_locked.
> This will allow to reuse this function in a next patch.
> 
> Signed-off-by: Cyrill Gorcunov <gorcunov@...nvz.org>
> Cc: Kees Cook <keescook@...omium.org>
> Cc: Tejun Heo <tj@...nel.org>
> Cc: Andrew Morton <akpm@...ux-foundation.org>
> Cc: Andrew Vagin <avagin@...nvz.org>
> Cc: Eric W. Biederman <ebiederm@...ssion.com>
> Cc: H. Peter Anvin <hpa@...or.com>
> Cc: Serge Hallyn <serge.hallyn@...onical.com>

Acked-by: Serge Hallyn <serge.hallyn@...onical.com>

> Cc: Pavel Emelyanov <xemul@...allels.com>
> Cc: Vasiliy Kulikov <segoon@...nwall.com>
> Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
> Cc: Michael Kerrisk <mtk.manpages@...il.com>
> Cc: Julien Tinnes <jln@...gle.com>
> ---
>  kernel/sys.c |   21 +++++++++++----------
>  1 file changed, 11 insertions(+), 10 deletions(-)
> 
> Index: linux-2.6.git/kernel/sys.c
> ===================================================================
> --- linux-2.6.git.orig/kernel/sys.c
> +++ linux-2.6.git/kernel/sys.c
> @@ -1628,12 +1628,14 @@ SYSCALL_DEFINE1(umask, int, mask)
>  	return mask;
>  }
>  
> -static int prctl_set_mm_exe_file(struct mm_struct *mm, unsigned int fd)
> +static int prctl_set_mm_exe_file_locked(struct mm_struct *mm, unsigned int fd)
>  {
>  	struct fd exe;
>  	struct inode *inode;
>  	int err;
>  
> +	VM_BUG_ON(!rwsem_is_locked(&mm->mmap_sem));
> +
>  	exe = fdget(fd);
>  	if (!exe.file)
>  		return -EBADF;
> @@ -1654,8 +1656,6 @@ static int prctl_set_mm_exe_file(struct
>  	if (err)
>  		goto exit;
>  
> -	down_write(&mm->mmap_sem);
> -
>  	/*
>  	 * Forbid mm->exe_file change if old file still mapped.
>  	 */
> @@ -1667,7 +1667,7 @@ static int prctl_set_mm_exe_file(struct
>  			if (vma->vm_file &&
>  			    path_equal(&vma->vm_file->f_path,
>  				       &mm->exe_file->f_path))
> -				goto exit_unlock;
> +				goto exit;
>  	}
>  
>  	/*
> @@ -1678,13 +1678,10 @@ static int prctl_set_mm_exe_file(struct
>  	 */
>  	err = -EPERM;
>  	if (test_and_set_bit(MMF_EXE_FILE_CHANGED, &mm->flags))
> -		goto exit_unlock;
> +		goto exit;
>  
>  	err = 0;
>  	set_mm_exe_file(mm, exe.file);	/* this grabs a reference to exe.file */
> -exit_unlock:
> -	up_write(&mm->mmap_sem);
> -
>  exit:
>  	fdput(exe);
>  	return err;
> @@ -1703,8 +1700,12 @@ static int prctl_set_mm(int opt, unsigne
>  	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_EXE_FILE) {
> +		down_write(&mm->mmap_sem);
> +		error = prctl_set_mm_exe_file_locked(mm, (unsigned int)addr);
> +		up_write(&mm->mmap_sem);
> +		return error;
> +	}
>  
>  	if (addr >= TASK_SIZE || addr < mmap_min_addr)
>  		return -EINVAL;
> 
> --
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