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Subject[tip: timers/core] posix-cpu-timers: Provide task validation functions
The following commit has been merged into the timers/core branch of tip:

Commit-ID: 6ae40e3fdcd33a6ff3c490b9302d6a1861093f65
Gitweb: https://git.kernel.org/tip/6ae40e3fdcd33a6ff3c490b9302d6a1861093f65
Author: Thomas Gleixner <tglx@linutronix.de>
AuthorDate: Wed, 21 Aug 2019 21:08:48 +02:00
Committer: Thomas Gleixner <tglx@linutronix.de>
CommitterDate: Wed, 28 Aug 2019 11:50:24 +02:00

posix-cpu-timers: Provide task validation functions

The code contains three slightly different copies of validating whether a
given clock resolves to a valid task and whether the current caller has
permissions to access it.

Create central functions. Replace check_clock() as a first step and rename
it to something sensible.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lkml.kernel.org/r/20190821192919.326097175@linutronix.de

---
kernel/time/posix-cpu-timers.c | 65 ++++++++++++++++++++++-----------
1 file changed, 44 insertions(+), 21 deletions(-)

diff --git a/kernel/time/posix-cpu-timers.c b/kernel/time/posix-cpu-timers.c
index 387e0e8..b06ed8b 100644
--- a/kernel/time/posix-cpu-timers.c
+++ b/kernel/time/posix-cpu-timers.c
@@ -35,27 +35,52 @@ void update_rlimit_cpu(struct task_struct *task, unsigned long rlim_new)
spin_unlock_irq(&task->sighand->siglock);
}

-static int check_clock(const clockid_t which_clock)
+/*
+ * Functions for validating access to tasks.
+ */
+static struct task_struct *lookup_task(const pid_t pid, bool thread)
{
- int error = 0;
struct task_struct *p;
- const pid_t pid = CPUCLOCK_PID(which_clock);

- if (CPUCLOCK_WHICH(which_clock) >= CPUCLOCK_MAX)
- return -EINVAL;
+ if (!pid)
+ return thread ? current : current->group_leader;
+
+ p = find_task_by_vpid(pid);
+ if (!p || p == current)
+ return p;
+ if (thread)
+ return same_thread_group(p, current) ? p : NULL;
+ if (p == current)
+ return p;
+ return has_group_leader_pid(p) ? p : NULL;
+}
+
+static struct task_struct *__get_task_for_clock(const clockid_t clock,
+ bool getref)
+{
+ const bool thread = !!CPUCLOCK_PERTHREAD(clock);
+ const pid_t pid = CPUCLOCK_PID(clock);
+ struct task_struct *p;

- if (pid == 0)
- return 0;
+ if (CPUCLOCK_WHICH(clock) >= CPUCLOCK_MAX)
+ return NULL;

rcu_read_lock();
- p = find_task_by_vpid(pid);
- if (!p || !(CPUCLOCK_PERTHREAD(which_clock) ?
- same_thread_group(p, current) : has_group_leader_pid(p))) {
- error = -EINVAL;
- }
+ p = lookup_task(pid, thread);
+ if (p && getref)
+ get_task_struct(p);
rcu_read_unlock();
+ return p;
+}

- return error;
+static inline struct task_struct *get_task_for_clock(const clockid_t clock)
+{
+ return __get_task_for_clock(clock, true);
+}
+
+static inline int validate_clock_permissions(const clockid_t clock)
+{
+ return __get_task_for_clock(clock, false) ? 0 : -EINVAL;
}

/*
@@ -125,7 +150,8 @@ static inline u64 virt_ticks(struct task_struct *p)
static int
posix_cpu_clock_getres(const clockid_t which_clock, struct timespec64 *tp)
{
- int error = check_clock(which_clock);
+ int error = validate_clock_permissions(which_clock);
+
if (!error) {
tp->tv_sec = 0;
tp->tv_nsec = ((NSEC_PER_SEC + HZ - 1) / HZ);
@@ -142,20 +168,17 @@ posix_cpu_clock_getres(const clockid_t which_clock, struct timespec64 *tp)
}

static int
-posix_cpu_clock_set(const clockid_t which_clock, const struct timespec64 *tp)
+posix_cpu_clock_set(const clockid_t clock, const struct timespec64 *tp)
{
+ int error = validate_clock_permissions(clock);
+
/*
* You can never reset a CPU clock, but we check for other errors
* in the call before failing with EPERM.
*/
- int error = check_clock(which_clock);
- if (error == 0) {
- error = -EPERM;
- }
- return error;
+ return error ? : -EPERM;
}

-
/*
* Sample a per-thread clock for the given task.
*/
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