From mboxrd@z Thu Jan 1 00:00:00 1970 Reply-To: kernel-hardening@lists.openwall.com Sender: Vasiliy Kulikov Date: Sun, 3 Jul 2011 14:39:25 +0400 From: Vasiliy Kulikov Message-ID: <20110703103925.GA2283@albatros> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Subject: [kernel-hardening] [PATCH] proc: fix a race in do_io_accounting() To: Linus Torvalds Cc: linux-kernel@vger.kernel.org, akpm@linux-foundation.org, viro@zeniv.linux.org.uk, rientjes@google.com, wilsons@start.ca, security@kernel.org, kernel-hardening@lists.openwall.com List-ID: 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(). Signed-off-by: Vasiliy Kulikov Cc: stable@kernel.org --- fs/proc/base.c | 10 ++++++++-- 1 files changed, 8 insertions(+), 2 deletions(-) diff --git a/fs/proc/base.c b/fs/proc/base.c index 083a4f2..c605ee1 100644 --- a/fs/proc/base.c +++ b/fs/proc/base.c @@ -2711,9 +2711,12 @@ 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 = -EACCES; + + mutex_lock(&task->signal->cred_guard_mutex); if (!ptrace_may_access(task, PTRACE_MODE_READ)) - return -EACCES; + goto out_unlock; if (whole && lock_task_sighand(task, &flags)) { struct task_struct *t = task; @@ -2724,7 +2727,7 @@ 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 +2742,9 @@ 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