It appears as though the addition of the PID namespace did not update the output code for /proc/*/sched, which resulted in it providing PIDs that were not self-consistent with the /proc mount. This additionally made it trivial to detect whether a process was inside &init_pid_ns from userspace (making container detection trivial[1]). This lead to situations such as:
% unshare -pmf % mount -t proc proc /proc % head -n1 /proc/1/sched head (10047, #threads: 1) Fix this by just using task_pid_nr_ns for the output of /proc/*/sched. All of the other uses of task_pid_nr in kernel/sched/debug.c are from a sysctl context and thus don't need to be namespaced. [1]: https://github.com/jessfraz/amicontained Cc: <sta...@vger.kernel.org> Cc: Jess Frazelle <acidb...@google.com> Signed-off-by: Aleksa Sarai <asa...@suse.com> --- fs/proc/base.c | 3 ++- include/linux/sched/debug.h | 4 +++- kernel/sched/debug.c | 5 +++-- 3 files changed, 8 insertions(+), 4 deletions(-) diff --git a/fs/proc/base.c b/fs/proc/base.c index 719c2e943ea1..98fd8f6df851 100644 --- a/fs/proc/base.c +++ b/fs/proc/base.c @@ -1408,12 +1408,13 @@ static const struct file_operations proc_fail_nth_operations = { static int sched_show(struct seq_file *m, void *v) { struct inode *inode = m->private; + struct pid_namespace *ns = inode->i_sb->s_fs_info; struct task_struct *p; p = get_proc_task(inode); if (!p) return -ESRCH; - proc_sched_show_task(p, m); + proc_sched_show_task(p, ns, m); put_task_struct(p); diff --git a/include/linux/sched/debug.h b/include/linux/sched/debug.h index e0eaee54c5a4..5d58d49e9f87 100644 --- a/include/linux/sched/debug.h +++ b/include/linux/sched/debug.h @@ -6,6 +6,7 @@ */ struct task_struct; +struct pid_namespace; extern void dump_cpu_task(int cpu); @@ -34,7 +35,8 @@ extern void sched_show_task(struct task_struct *p); #ifdef CONFIG_SCHED_DEBUG struct seq_file; -extern void proc_sched_show_task(struct task_struct *p, struct seq_file *m); +extern void proc_sched_show_task(struct task_struct *p, + struct pid_namespace *ns, struct seq_file *m); extern void proc_sched_set_task(struct task_struct *p); #endif diff --git a/kernel/sched/debug.c b/kernel/sched/debug.c index 4fa66de52bd6..ac345115877b 100644 --- a/kernel/sched/debug.c +++ b/kernel/sched/debug.c @@ -872,11 +872,12 @@ static void sched_show_numa(struct task_struct *p, struct seq_file *m) #endif } -void proc_sched_show_task(struct task_struct *p, struct seq_file *m) +void proc_sched_show_task(struct task_struct *p, struct pid_namespace *ns, + struct seq_file *m) { unsigned long nr_switches; - SEQ_printf(m, "%s (%d, #threads: %d)\n", p->comm, task_pid_nr(p), + SEQ_printf(m, "%s (%d, #threads: %d)\n", p->comm, task_pid_nr_ns(p, ns), get_nr_threads(p)); SEQ_printf(m, "---------------------------------------------------------" -- 2.13.3
