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Subject[PATCH] posix_cpu_timers: fix timer never expires when executes clock_nanosleep
From c7439b90b0794c016b29356f0e232f7413ef7b60 Mon Sep 17 00:00:00 2001
From: Dong Zhu <bluezhudong@gmail.com>
Date: Thu, 1 Aug 2013 11:39:04 +0800

When use the current process pid as the clockid, then executes
clock_nanosleep syscall the timer will never expire. Kernel should
prevent user doing like this and this patch is supposed to fix it.I
wrote a simple case to test it:

#include <time.h>
#include <errno.h>
#include <unistd.h>
#include <sys/types.h>

#define CPU_CLOCK_PROF 0
#define CPU_CLOCK_VIRT 1
#define CPU_CLOCK_SCHED 2

#define CPU_CLOCK_THREAD 4
#define PID_TO_CLOCKID(pid, clock) ((~(clockid_t) (pid) << 3) | (clockid_t) (clock))

int main(void)
{
int ret;
pid_t pid;
clockid_t clk;
struct timespec ts;

ts.tv_sec = 1;
ts.tv_nsec = 0;

pid = getpid();
clk = PID_TO_CLOCKID(pid, CPU_CLOCK_PROF);
if ((ret = clock_nanosleep(clk, 0, &ts, NULL)) != 0) {
perror("clock_nanosleep");
return ret;
}

return 0;
}

Signed-off-by: Dong Zhu <bluezhudong@gmail.com>
---
kernel/posix-cpu-timers.c | 6 +++---
1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/kernel/posix-cpu-timers.c b/kernel/posix-cpu-timers.c
index c7f31aa..cc03290 100644
--- a/kernel/posix-cpu-timers.c
+++ b/kernel/posix-cpu-timers.c
@@ -1413,9 +1413,9 @@ static int posix_cpu_nsleep(const clockid_t which_clock, int flags,
/*
* Diagnose required errors first.
*/
- if (CPUCLOCK_PERTHREAD(which_clock) &&
- (CPUCLOCK_PID(which_clock) == 0 ||
- CPUCLOCK_PID(which_clock) == current->pid))
+ if (CPUCLOCK_PID(which_clock) == current->pid ||
+ (CPUCLOCK_PERTHREAD(which_clock) &&
+ CPUCLOCK_PID(which_clock) == 0))
return -EINVAL;

error = do_cpu_nanosleep(which_clock, flags, rqtp, &it);
--
1.7.11.7

--
Best Regards,
Dong Zhu


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