Messages in this thread Patch in this message | | | Date | Mon, 23 Sep 2019 16:54:37 +0200 | From | Thomas Gleixner <> | Subject | [patch V2 2/6] posix-cpu-timers: Restrict clock_gettime() permissions |
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From: Thomas Gleixner <tglx@linutronix.de>
Similar to creating timers on a process there is no restriction at all to read the Posix CPU clocks of any process in the system. Per thread CPU clock access is limited to threads in the same thread group.
The per process CPU clocks can be used to observe activity of tasks and reading them can affect the execution of the process to which they are attached as reading can require to lock sighand lock and sum up the fine grained accounting for all threads in the process.
Restrict it by checking ptrace MODE_READ permissions of the reader on the target process.
Signed-off-by: Thomas Gleixner <tglx@linutronix.de> Reviewed-by: Frederic Weisbecker <frederic@kernel.org> --- kernel/time/posix-cpu-timers.c | 13 ++++++++++++- 1 file changed, 12 insertions(+), 1 deletion(-)
--- a/kernel/time/posix-cpu-timers.c +++ b/kernel/time/posix-cpu-timers.c @@ -76,8 +76,19 @@ static struct task_struct *lookup_task(c * Timers need the group leader because they take a * reference on it and store the task pointer until the * timer is destroyed. + * + * current can obviously access it's own process, so spare + * the ptrace check below. */ - return (p == current || thread_group_leader(p)) ? p : NULL; + if (p == current) + return p; + + if (!thread_group_leader(p)) + return NULL; + + if (!ptrace_may_access(p, PTRACE_MODE_READ_REALCREDS)) + return NULL; + return p; } /*
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