linux-kernel - Re: [TOMOYO #16 01/25] LSM: Add security_path_chmod() and security_path

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Message-ID: <20091029051211.GB11558@us.ibm.com>
Date:	Thu, 29 Oct 2009 00:12:11 -0500
From:	"Serge E. Hallyn" <serue@...ibm.com>
To:	Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
Cc:	linux-security-module@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [TOMOYO #16 01/25] LSM: Add security_path_chmod() and
	security_path_chown().

Quoting Tetsuo Handa (penguin-kernel@...ove.SAKURA.ne.jp):
> This patch allows pathname based LSM modules to check chmod()/chown()
> operations. Since notify_change() does not receive "struct vfsmount *",
> we add security_path_chmod() and security_path_chown() to the caller of
> notify_change().
> 
> These hooks are used by TOMOYO.
> 
> Signed-off-by: Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
> ---
>  fs/open.c                |   24 ++++++++++++++++++++----
>  include/linux/security.h |   30 ++++++++++++++++++++++++++++++
>  security/capability.c    |   13 +++++++++++++
>  security/security.c      |   15 +++++++++++++++
>  4 files changed, 78 insertions(+), 4 deletions(-)
> 
> --- security-testing-2.6.orig/fs/open.c
> +++ security-testing-2.6/fs/open.c
> @@ -616,6 +616,9 @@ SYSCALL_DEFINE2(fchmod, unsigned int, fd
>  	err = mnt_want_write_file(file);
>  	if (err)
>  		goto out_putf;
> +	err = security_path_chmod(dentry, file->f_vfsmnt, mode);
> +	if (err)
> +		goto out_drop_write;
>  	mutex_lock(&inode->i_mutex);

Isn't doing the security check before the mutex_lock racy?

Any reason not to move it into the lock?  (since you had
considered putting a path hook in notify_change() I assume
not?)

-serge
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