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Message-Id: <1380140085-29712-8-git-send-email-tixxdz@opendz.org>
Date: Wed, 25 Sep 2013 21:14:40 +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>,
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 07/12] procfs: add permission checks on the file's opener of /proc/*/stack
/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().
Use proc_same_open_cred() to detect if the cred of current between
->open() and ->read() have changed, if so then call proc_allow_access()
to check if the original file's opener had enough privileges to access
the /proc's task entries during ->read().
The file's opener cred are obtained by seq_f_cred() on seq_file struct.
The ptrace_may_access() + proc_allow_access() check is performed during
->read() time, where the ptrace_may_access() check should also be
performed during ->open(), however currently this is not the case.
This is due to /procfs ONE files that share the same ->open() function
proc_single_open(). Adding the ptrace_may_access() check to
proc_single_open() might break userspace from accessing other ONE files
like /proc/*/stat and /proc/*/statm.
So just perform the checks during ->read() and if current's cred have
changed, then check the file's opener cred with proc_allow_access().
This will block passing the file descriptor to a more privileged
process (e.g. a suid-exec).
Cc: Kees Cook <keescook@...omium.org>
Cc: Eric W. Biederman <ebiederm@...ssion.com>
Signed-off-by: Djalal Harouni <tixxdz@...ndz.org>
---
fs/proc/base.c | 26 +++++++++++++++++++-------
1 file changed, 19 insertions(+), 7 deletions(-)
diff --git a/fs/proc/base.c b/fs/proc/base.c
index bb90171..d6a17b3 100644
--- a/fs/proc/base.c
+++ b/fs/proc/base.c
@@ -402,6 +402,8 @@ static int proc_pid_stack(struct seq_file *m, struct pid_namespace *ns,
unsigned long *entries;
int err;
int i;
+ int same_cred;
+ const struct cred *fcred = seq_f_cred(m);
entries = kmalloc(MAX_STACK_TRACE_DEPTH * sizeof(*entries), GFP_KERNEL);
if (!entries)
@@ -412,18 +414,28 @@ static int proc_pid_stack(struct seq_file *m, struct pid_namespace *ns,
trace.entries = entries;
trace.skip = 0;
+ same_cred = proc_same_open_cred(fcred);
+
err = lock_trace(task);
- if (!err) {
- save_stack_trace_tsk(task, &trace);
+ if (err)
+ goto free;
- for (i = 0; i < trace.nr_entries; i++) {
- seq_printf(m, "[<%pK>] %pS\n",
- (void *)entries[i], (void *)entries[i]);
- }
+ if (!same_cred && !proc_allow_access(fcred, task, PTRACE_MODE_ATTACH)) {
+ err = -EPERM;
unlock_trace(task);
+ goto free;
}
- kfree(entries);
+ save_stack_trace_tsk(task, &trace);
+ unlock_trace(task);
+
+ for (i = 0; i < trace.nr_entries; i++) {
+ seq_printf(m, "[<%pK>] %pS\n",
+ (void *)entries[i], (void *)entries[i]);
+ }
+
+free:
+ kfree(entries);
return err;
}
#endif
--
1.7.11.7
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