This is a note to let you know that I've just added the patch titled
proc: fix a race in do_io_accounting()
to the 3.0-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
proc-fix-a-race-in-do_io_accounting.patch
and it can be found in the queue-3.0 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <sta...@kernel.org> know about it.
>From 293eb1e7772b25a93647c798c7b89bf26c2da2e0 Mon Sep 17 00:00:00 2001
From: Vasiliy Kulikov <seg...@openwall.com>
Date: Tue, 26 Jul 2011 16:08:38 -0700
Subject: proc: fix a race in do_io_accounting()
From: Vasiliy Kulikov <seg...@openwall.com>
commit 293eb1e7772b25a93647c798c7b89bf26c2da2e0 upstream.
If an inode's mode permits opening /proc/PID/io and the resulting file
descriptor is kept across execve() of a setuid or similar binary, the
ptrace_may_access() check tries to prevent using this fd against the
task with escalated privileges.
Unfortunately, there is a race in the check against execve(). If
execve() is processed after the ptrace check, but before the actual io
information gathering, io statistics will be gathered from the
privileged process. At least in theory this might lead to gathering
sensible information (like ssh/ftp password length) that wouldn't be
available otherwise.
Holding task->signal->cred_guard_mutex while gathering the io
information should protect against the race.
The order of locking is similar to the one inside of ptrace_attach():
first goes cred_guard_mutex, then lock_task_sighand().
Signed-off-by: Vasiliy Kulikov <seg...@openwall.com>
Cc: Al Viro <v...@zeniv.linux.org.uk>
Signed-off-by: Andrew Morton <a...@linux-foundation.org>
Signed-off-by: Linus Torvalds <torva...@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gre...@suse.de>
---
fs/proc/base.c | 16 +++++++++++++---
1 file changed, 13 insertions(+), 3 deletions(-)
--- a/fs/proc/base.c
+++ b/fs/proc/base.c
@@ -2707,9 +2707,16 @@ static int do_io_accounting(struct task_
{
struct task_io_accounting acct = task->ioac;
unsigned long flags;
+ int result;
- if (!ptrace_may_access(task, PTRACE_MODE_READ))
- return -EACCES;
+ result = mutex_lock_killable(&task->signal->cred_guard_mutex);
+ if (result)
+ return result;
+
+ if (!ptrace_may_access(task, PTRACE_MODE_READ)) {
+ result = -EACCES;
+ goto out_unlock;
+ }
if (whole && lock_task_sighand(task, &flags)) {
struct task_struct *t = task;
@@ -2720,7 +2727,7 @@ static int do_io_accounting(struct task_
unlock_task_sighand(task, &flags);
}
- return sprintf(buffer,
+ result = sprintf(buffer,
"rchar: %llu\n"
"wchar: %llu\n"
"syscr: %llu\n"
@@ -2735,6 +2742,9 @@ static int do_io_accounting(struct task_
(unsigned long long)acct.read_bytes,
(unsigned long long)acct.write_bytes,
(unsigned long long)acct.cancelled_write_bytes);
+out_unlock:
+ mutex_unlock(&task->signal->cred_guard_mutex);
+ return result;
}
static int proc_tid_io_accounting(struct task_struct *task, char *buffer)
Patches currently in stable-queue which might be from seg...@openwall.com are
queue-3.0/proc-fix-a-race-in-do_io_accounting.patch
queue-3.0/staging-comedi-fix-infoleak-to-userspace.patch
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