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Message-Id: <1380659178-28605-7-git-send-email-tixxdz@opendz.org>
Date: Tue, 1 Oct 2013 21:26:15 +0100
From: Djalal Harouni <tixxdz@...ndz.org>
To: "Eric W. Biederman" <ebiederm@...ssion.com>,
Kees Cook <keescook@...omium.org>,
Al Viro <viro@...iv.linux.org.uk>,
Andrew Morton <akpm@...ux-foundation.org>,
Linus Torvalds <torvalds@...ux-foundation.org>,
Ingo Molnar <mingo@...nel.org>,
"Serge E. Hallyn" <serge.hallyn@...ntu.com>,
Cyrill Gorcunov <gorcunov@...nvz.org>,
David Rientjes <rientjes@...gle.com>,
LKML <linux-kernel@...r.kernel.org>,
linux-fsdevel@...r.kernel.org,
kernel-hardening@...ts.openwall.com
Cc: tixxdz@...il.com,
Djalal Harouni <tixxdz@...ndz.org>
Subject: [PATCH v2 6/9] procfs: add permission checks on the file's opener of /proc/*/stat
Some fields of the /proc/*/stat are sensitive fields that need
appropriate protection.
However, /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 during read().
To prevent it, use proc_same_open_cred() to detect if current's cred
have changed between ->open() and ->read(), if so, call
proc_allow_access() to check if the original file's opener had enough
permissions to read these sensitive fields. This will prevent passing
file descriptors to a more privileged process to leak data.
The patch also adds a previously missing signal->cred_guard_mutex lock.
This patch does not break userspace since it only hides the fields that
were supposed to be protected.
Cc: Kees Cook <keescook@...omium.org>
Cc: Eric W. Biederman <ebiederm@...ssion.com>
Signed-off-by: Djalal Harouni <tixxdz@...ndz.org>
---
fs/proc/array.c | 16 ++++++++++++++--
1 file changed, 14 insertions(+), 2 deletions(-)
diff --git a/fs/proc/array.c b/fs/proc/array.c
index cbd0f1b..f034e05 100644
--- a/fs/proc/array.c
+++ b/fs/proc/array.c
@@ -394,7 +394,7 @@ static int do_task_stat(struct seq_file *m, struct pid_namespace *ns,
char state;
pid_t ppid = 0, pgid = -1, sid = -1;
int num_threads = 0;
- int permitted;
+ int permitted = 0;
struct mm_struct *mm;
unsigned long long start_time;
unsigned long cmin_flt = 0, cmaj_flt = 0;
@@ -404,10 +404,22 @@ static int do_task_stat(struct seq_file *m, struct pid_namespace *ns,
unsigned long rsslim = 0;
char tcomm[sizeof(task->comm)];
unsigned long flags;
+ struct file *file = m->private;
+ int same_cred = proc_same_open_cred(file->f_cred);
+ unsigned int ptrace_mode = PTRACE_MODE_READ | PTRACE_MODE_NOAUDIT;
state = *get_task_state(task);
vsize = eip = esp = 0;
- permitted = ptrace_may_access(task, PTRACE_MODE_READ | PTRACE_MODE_NOAUDIT);
+
+ if (!mutex_lock_killable(&task->signal->cred_guard_mutex)) {
+ permitted = ptrace_may_access(task, ptrace_mode);
+ if (permitted && !same_cred)
+ permitted = proc_allow_access(file->f_cred,
+ task, ptrace_mode);
+
+ mutex_unlock(&task->signal->cred_guard_mutex);
+ }
+
mm = get_task_mm(task);
if (mm) {
vsize = task_vsize(mm);
--
1.7.11.7
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