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Date: Tue, 5 Jul 2011 00:13:39 +0400
From: Vasiliy Kulikov <segoon@...nwall.com>
To: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: linux-kernel@...r.kernel.org, akpm@...ux-foundation.org,
viro@...iv.linux.org.uk, rientjes@...gle.com, wilsons@...rt.ca,
security@...nel.org, kernel-hardening@...ts.openwall.com
Subject: [PATCH v2] proc: fix a race in do_io_accounting()
There is a ptrace_may_access() check in do_io_accounting() to prevent
gathering information of setuid'ed and similar binaries. However, there
is a race against execve(). Holding task->signal->cred_guard_mutex
while gathering the 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().
v2 - use mutex_lock_killable() instead of mutex_lock().
Signed-off-by: Vasiliy Kulikov <segoon@...nwall.com>
Cc: stable@...nel.org
---
fs/proc/base.c | 16 +++++++++++++---
1 files changed, 13 insertions(+), 3 deletions(-)
diff --git a/fs/proc/base.c b/fs/proc/base.c
index 083a4f2..4b9f159 100644
--- a/fs/proc/base.c
+++ b/fs/proc/base.c
@@ -2711,9 +2711,16 @@ static int do_io_accounting(struct task_struct *task, char *buffer, int whole)
{
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;
@@ -2724,7 +2731,7 @@ static int do_io_accounting(struct task_struct *task, char *buffer, int whole)
unlock_task_sighand(task, &flags);
}
- return sprintf(buffer,
+ result = sprintf(buffer,
"rchar: %llu\n"
"wchar: %llu\n"
"syscr: %llu\n"
@@ -2739,6 +2746,9 @@ static int do_io_accounting(struct task_struct *task, char *buffer, int whole)
(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)
--
1.7.0.4
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