linux-kernel - Re: [PATCH v2] fs: clear file privilege bits when mmap writing

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-Id: <20151202161851.95d8fe811705c038e3fe2d33@linux-foundation.org>
Date:	Wed, 2 Dec 2015 16:18:51 -0800
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Kees Cook <keescook@...omium.org>
Cc:	Jan Kara <jack@...e.cz>, Willy Tarreau <w@....eu>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
	Oleg Nesterov <oleg@...hat.com>,
	Rik van Riel <riel@...hat.com>,
	Chen Gang <gang.chen.5i5j@...il.com>,
	Davidlohr Bueso <dave@...olabs.net>,
	Andrea Arcangeli <aarcange@...hat.com>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] fs: clear file privilege bits when mmap writing

On Wed, 2 Dec 2015 16:03:42 -0800 Kees Cook <keescook@...omium.org> wrote:

> Normally, when a user can modify a file that has setuid or setgid bits,
> those bits are cleared when they are not the file owner or a member
> of the group. This is enforced when using write and truncate but not
> when writing to a shared mmap on the file. This could allow the file
> writer to gain privileges by changing a binary without losing the
> setuid/setgid/caps bits.
> 
> Changing the bits requires holding inode->i_mutex, so it cannot be done
> during the page fault (due to mmap_sem being held during the fault).
> Instead, clear the bits if PROT_WRITE is being used at mmap time.
> 
> ...
>
> --- a/mm/mmap.c
> +++ b/mm/mmap.c
> @@ -1340,6 +1340,17 @@ unsigned long do_mmap(struct file *file, unsigned long addr,
>  			if (locks_verify_locked(file))
>  				return -EAGAIN;
>  
> +			/*
> +			 * If we must remove privs, we do it here since
> +			 * doing it during page COW is expensive and
> +			 * cannot hold inode->i_mutex.
> +			 */
> +			if (prot & PROT_WRITE && !IS_NOSEC(inode)) {
> +				mutex_lock(&inode->i_mutex);
> +				file_remove_privs(file);
> +				mutex_unlock(&inode->i_mutex);
> +			}
> +

Still ignoring the file_remove_privs() return value.  If this is
deliberate then a description of the reasons should be included?

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/