Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755545Ab3IYUSl (ORCPT ); Wed, 25 Sep 2013 16:18:41 -0400 Received: from numidia.opendz.org ([98.142.220.152]:33250 "EHLO numidia.opendz.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755261Ab3IYUSj (ORCPT ); Wed, 25 Sep 2013 16:18:39 -0400 From: Djalal Harouni To: "Eric W. Biederman" , Kees Cook , Al Viro , Andrew Morton , Linus Torvalds , Ingo Molnar , "Serge E. Hallyn" , Cyrill Gorcunov , LKML , linux-fsdevel@vger.kernel.org, Cc: tixxdz@gmail.com, Djalal Harouni Subject: [PATCH 02/12] procfs: add proc_allow_access() to check if file's opener may access task Date: Wed, 25 Sep 2013 21:14:35 +0100 Message-Id: <1380140085-29712-3-git-send-email-tixxdz@opendz.org> X-Mailer: git-send-email 1.7.11.7 In-Reply-To: <1380140085-29712-1-git-send-email-tixxdz@opendz.org> References: <1380140085-29712-1-git-send-email-tixxdz@opendz.org> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 4040 Lines: 117 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 Cc: 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; + + if (mode & PTRACE_MODE_NOAUDIT) + ret = security_capable_noaudit(fcred, tcred->user_ns, + CAP_SYS_PTRACE); + else + ret = security_capable(fcred, tcred->user_ns, + CAP_SYS_PTRACE); + +out: + rcu_read_unlock(); + return !ret ? ret : -EPERM; +} + +/** + * proc_allow_access - Check if the file's opener had enough permissions + * to access the target process. + * @fcred: The file's opener cred (file->f_cred) + * @task: The target task we want to inspect + * @mode: The ptrace mode + * + * Return a non-zero if the file's opener had enough permissions to + * access the task's /proc entries. + * + * Since this function will check the permissions of the opener + * against the target task, it can be used to protect /proc files + * from opening a /proc file descriptor and do a suid-exec. + * + * Callers must hold the task->signal->cred_guard_mutex + */ +int proc_allow_access(const struct cred *fcred, + struct task_struct *task, unsigned int mode) +{ + int ret; + task_lock(task); + ret = __proc_allow_access(fcred, task, mode); + task_unlock(task); + return !ret; +} + /* * Count the number of hardlinks for the pid_entry table, excluding the . * and .. links. diff --git a/fs/proc/internal.h b/fs/proc/internal.h index e2459f4..c3f3c34 100644 --- a/fs/proc/internal.h +++ b/fs/proc/internal.h @@ -159,6 +159,8 @@ extern int proc_pid_statm(struct seq_file *, struct pid_namespace *, /* * base.c */ +extern int proc_allow_access(const struct cred *, + struct task_struct *, unsigned int); extern int proc_same_open_cred(const struct cred *); extern const struct dentry_operations pid_dentry_operations; extern int pid_getattr(struct vfsmount *, struct dentry *, struct kstat *); -- 1.7.11.7 -- 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/