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Subject[PATCH] do_task_stat: don't use task_pid_nr_ns() lockless
Without rcu/tasklist/siglock lock task_pid_nr_ns() may read the freed memory,
move the callsite under ->siglock.

Sadly, we can report pid == 0 if the task was detached.

Signed-off-by: Oleg Nesterov <oleg@tv-sign.ru>

--- 24/fs/proc/array.c~dtst 2007-11-09 12:57:30.000000000 +0300
+++ 24/fs/proc/array.c 2007-11-17 21:26:55.000000000 +0300
@@ -392,7 +392,7 @@ static int do_task_stat(struct task_stru
sigset_t sigign, sigcatch;
char state;
int res;
- pid_t ppid = 0, pgid = -1, sid = -1;
+ pid_t pid = 0, ppid = 0, pgid = -1, sid = -1;
int num_threads = 0;
struct mm_struct *mm;
unsigned long long start_time;
@@ -403,9 +403,6 @@ static int do_task_stat(struct task_stru
unsigned long rsslim = 0;
char tcomm[sizeof(task->comm)];
unsigned long flags;
- struct pid_namespace *ns;
-
- ns = current->nsproxy->pid_ns;

state = *get_task_state(task);
vsize = eip = esp = 0;
@@ -425,6 +422,7 @@ static int do_task_stat(struct task_stru

rcu_read_lock();
if (lock_task_sighand(task, &flags)) {
+ struct pid_namespace *ns = current->nsproxy->pid_ns;
struct signal_struct *sig = task->signal;

if (sig->tty) {
@@ -461,6 +459,7 @@ static int do_task_stat(struct task_stru
gtime = cputime_add(gtime, sig->gtime);
}

+ pid = task_pid_nr_ns(task, ns);
sid = task_session_nr_ns(task, ns);
pgid = task_pgrp_nr_ns(task, ns);
ppid = task_ppid_nr_ns(task, ns);
@@ -495,7 +494,7 @@ static int do_task_stat(struct task_stru
res = sprintf(buffer, "%d (%s) %c %d %d %d %d %d %u %lu \
%lu %lu %lu %lu %lu %ld %ld %ld %ld %d 0 %llu %lu %ld %lu %lu %lu %lu %lu \
%lu %lu %lu %lu %lu %lu %lu %lu %d %d %u %u %llu %lu %ld\n",
- task_pid_nr_ns(task, ns),
+ pid,
tcomm,
state,
ppid,
-
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