Re: [PATCH] LSM: Move security_path_chmod()/security_path_chown() to after mutex_lock().

[John Johansen <john.johansen@canonical.com>]

Tetsuo Handa wrote:
> [PATCH] LSM: Move security_path_chmod()/security_path_chown() to after mutex_lock().
> 
> We should call security_path_chmod()/security_path_chown() after mutex_lock()
> in order to avoid races.
> 
> Signed-off-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>

Acked-by: John Johansen <john.johansen@canonical.com>

> ---
>  fs/open.c |   36 +++++++++++++++---------------------
>  1 file changed, 15 insertions(+), 21 deletions(-)
> 
> --- security-testing-2.6.orig/fs/open.c
> +++ security-testing-2.6/fs/open.c
> @@ -619,17 +619,17 @@ SYSCALL_DEFINE2(fchmod, unsigned int, fd
>  	err = mnt_want_write_file(file);
>  	if (err)
>  		goto out_putf;
> +	mutex_lock(&inode->i_mutex);
>  	err = security_path_chmod(dentry, file->f_vfsmnt, mode);
>  	if (err)
> -		goto out_drop_write;
> -	mutex_lock(&inode->i_mutex);
> +		goto out_unlock;
>  	if (mode == (mode_t) -1)
>  		mode = inode->i_mode;
>  	newattrs.ia_mode = (mode & S_IALLUGO) | (inode->i_mode & ~S_IALLUGO);
>  	newattrs.ia_valid = ATTR_MODE | ATTR_CTIME;
>  	err = notify_change(dentry, &newattrs);
> +out_unlock:
>  	mutex_unlock(&inode->i_mutex);
> -out_drop_write:
>  	mnt_drop_write(file->f_path.mnt);
>  out_putf:
>  	fput(file);
> @@ -652,17 +652,17 @@ SYSCALL_DEFINE3(fchmodat, int, dfd, cons
>  	error = mnt_want_write(path.mnt);
>  	if (error)
>  		goto dput_and_out;
> +	mutex_lock(&inode->i_mutex);
>  	error = security_path_chmod(path.dentry, path.mnt, mode);
>  	if (error)
> -		goto out_drop_write;
> -	mutex_lock(&inode->i_mutex);
> +		goto out_unlock;
>  	if (mode == (mode_t) -1)
>  		mode = inode->i_mode;
>  	newattrs.ia_mode = (mode & S_IALLUGO) | (inode->i_mode & ~S_IALLUGO);
>  	newattrs.ia_valid = ATTR_MODE | ATTR_CTIME;
>  	error = notify_change(path.dentry, &newattrs);
> +out_unlock:
>  	mutex_unlock(&inode->i_mutex);
> -out_drop_write:
>  	mnt_drop_write(path.mnt);
>  dput_and_out:
>  	path_put(&path);
> @@ -675,9 +675,9 @@ SYSCALL_DEFINE2(chmod, const char __user
>  	return sys_fchmodat(AT_FDCWD, filename, mode);
>  }
>  
> -static int chown_common(struct dentry * dentry, uid_t user, gid_t group)
> +static int chown_common(struct path *path, uid_t user, gid_t group)
>  {
> -	struct inode *inode = dentry->d_inode;
> +	struct inode *inode = path->dentry->d_inode;
>  	int error;
>  	struct iattr newattrs;
>  
> @@ -694,7 +694,9 @@ static int chown_common(struct dentry * 
>  		newattrs.ia_valid |=
>  			ATTR_KILL_SUID | ATTR_KILL_SGID | ATTR_KILL_PRIV;
>  	mutex_lock(&inode->i_mutex);
> -	error = notify_change(dentry, &newattrs);
> +	error = security_path_chown(path, user, group);
> +	if (!error)
> +		error = notify_change(path->dentry, &newattrs);
>  	mutex_unlock(&inode->i_mutex);
>  
>  	return error;
> @@ -711,9 +713,7 @@ SYSCALL_DEFINE3(chown, const char __user
>  	error = mnt_want_write(path.mnt);
>  	if (error)
>  		goto out_release;
> -	error = security_path_chown(&path, user, group);
> -	if (!error)
> -		error = chown_common(path.dentry, user, group);
> +	error = chown_common(&path, user, group);
>  	mnt_drop_write(path.mnt);
>  out_release:
>  	path_put(&path);
> @@ -738,9 +738,7 @@ SYSCALL_DEFINE5(fchownat, int, dfd, cons
>  	error = mnt_want_write(path.mnt);
>  	if (error)
>  		goto out_release;
> -	error = security_path_chown(&path, user, group);
> -	if (!error)
> -		error = chown_common(path.dentry, user, group);
> +	error = chown_common(&path, user, group);
>  	mnt_drop_write(path.mnt);
>  out_release:
>  	path_put(&path);
> @@ -759,9 +757,7 @@ SYSCALL_DEFINE3(lchown, const char __use
>  	error = mnt_want_write(path.mnt);
>  	if (error)
>  		goto out_release;
> -	error = security_path_chown(&path, user, group);
> -	if (!error)
> -		error = chown_common(path.dentry, user, group);
> +	error = chown_common(&path, user, group);
>  	mnt_drop_write(path.mnt);
>  out_release:
>  	path_put(&path);
> @@ -784,9 +780,7 @@ SYSCALL_DEFINE3(fchown, unsigned int, fd
>  		goto out_fput;
>  	dentry = file->f_path.dentry;
>  	audit_inode(NULL, dentry);
> -	error = security_path_chown(&file->f_path, user, group);
> -	if (!error)
> -		error = chown_common(dentry, user, group);
> +	error = chown_common(&file->f_path, user, group);
>  	mnt_drop_write(file->f_path.mnt);
>  out_fput:
>  	fput(file);
> 
> --
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