From mboxrd@z Thu Jan 1 00:00:00 1970 Reply-To: kernel-hardening@lists.openwall.com Message-ID: <524B78A2.40007@amacapital.net> Date: Tue, 01 Oct 2013 18:36:34 -0700 From: Andy Lutomirski MIME-Version: 1.0 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 Subject: [kernel-hardening] Re: [PATCH v2 2/9] procfs: add proc_allow_access() to check if file's opener may access task 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 List-ID: 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 From mboxrd@z Thu Jan 1 00:00:00 1970 From: Andy Lutomirski Subject: Re: [PATCH v2 2/9] procfs: add proc_allow_access() to check if file's opener may access task Date: Tue, 01 Oct 2013 18:36:34 -0700 Message-ID: <524B78A2.40007@amacapital.net> References: <1380659178-28605-1-git-send-email-tixxdz@opendz.org> <1380659178-28605-3-git-send-email-tixxdz@opendz.org> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit 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 To: Djalal Harouni Return-path: In-Reply-To: <1380659178-28605-3-git-send-email-tixxdz@opendz.org> Sender: linux-kernel-owner@vger.kernel.org List-Id: linux-fsdevel.vger.kernel.org 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