Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752650Ab3JBBgk (ORCPT ); Tue, 1 Oct 2013 21:36:40 -0400 Received: from mail-pa0-f46.google.com ([209.85.220.46]:40890 "EHLO mail-pa0-f46.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751786Ab3JBBgh (ORCPT ); Tue, 1 Oct 2013 21:36:37 -0400 Message-ID: <524B78A2.40007@amacapital.net> Date: Tue, 01 Oct 2013 18:36:34 -0700 From: Andy Lutomirski User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:17.0) Gecko/20130923 Thunderbird/17.0.9 MIME-Version: 1.0 To: Djalal Harouni CC: "Eric W. Biederman" , Kees Cook , Al Viro , Andrew Morton , Linus Torvalds , Ingo Molnar , "Serge E. Hallyn" , Cyrill Gorcunov , David Rientjes , LKML , linux-fsdevel@vger.kernel.org, kernel-hardening@lists.openwall.com, tixxdz@gmail.com Subject: Re: [PATCH v2 2/9] procfs: add proc_allow_access() to check if file's opener may access task References: <1380659178-28605-1-git-send-email-tixxdz@opendz.org> <1380659178-28605-3-git-send-email-tixxdz@opendz.org> In-Reply-To: <1380659178-28605-3-git-send-email-tixxdz@opendz.org> Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2624 Lines: 67 On 10/01/2013 01:26 PM, Djalal Harouni wrote: > Since /proc entries varies at runtime, permission checks need to happen > during each system call. > > However even with that /proc file descriptors can be passed to a more > privileged process (e.g. a suid-exec) which will pass the classic > ptrace_may_access() permission check. The open() call will be issued in > general by an unprivileged process while the disclosure of sensitive > /proc information will happen using a more privileged process at > read(),write()... > > Therfore we need a more sophisticated check to detect if the cred of the > process have changed, and if the cred of the original opener that are > stored in the file->f_cred have enough permission to access the task's > /proc entries during read(), write()... > > Add the proc_allow_access() function that will receive the file->f_cred > as an argument, and tries to check if the opener had enough permission > to access the task's /proc entries. > > This function should be used with the ptrace_may_access() check. > > Cc: Kees Cook > Suggested-by: Eric W. Biederman > Signed-off-by: Djalal Harouni > --- > fs/proc/base.c | 56 ++++++++++++++++++++++++++++++++++++++++++++++++++++++ > fs/proc/internal.h | 2 ++ > 2 files changed, 58 insertions(+) > > diff --git a/fs/proc/base.c b/fs/proc/base.c > index e834946..c29eeae 100644 > --- a/fs/proc/base.c > +++ b/fs/proc/base.c > @@ -168,6 +168,62 @@ int proc_same_open_cred(const struct cred *fcred) > cap_issubset(cred->cap_permitted, fcred->cap_permitted)); > } > > +/* Returns 0 on success, -errno on denial. */ > +static int __proc_allow_access(const struct cred *cred, > + struct task_struct *task, unsigned int mode) > +{ > + int ret = 0; > + const struct cred *tcred; > + const struct cred *fcred = cred; > + > + rcu_read_lock(); > + tcred = __task_cred(task); > + if (uid_eq(fcred->uid, tcred->euid) && > + uid_eq(fcred->uid, tcred->suid) && > + uid_eq(fcred->uid, tcred->uid) && > + gid_eq(fcred->gid, tcred->egid) && > + gid_eq(fcred->gid, tcred->sgid) && > + gid_eq(fcred->gid, tcred->gid)) > + goto out; > + What's this for? Is it supposed to be an optimization? If so, it looks potentially exploitable, although I don't really understand what you're trying to do. --Andy -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/