[PATCH v5 5/7] proc: instantiate only pids that we can ptrace on 'limit_pids=1' mount option

[Alexey Gladkov]

From: Djalal Harouni <tix...@gmail.com>

If "limit_pids=1" mount option is set then do not instantiate pids that
we can not ptrace. "limit_pids=1" means that procfs should only contain
pids that the caller can ptrace.

Cc: Kees Cook <keesc...@chromium.org>
Cc: Andy Lutomirski <l...@kernel.org>
Signed-off-by: Djalal Harouni <tix...@gmail.com>
---
 fs/proc/base.c | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/fs/proc/base.c b/fs/proc/base.c
index 6f084344..31baeef 100644
--- a/fs/proc/base.c
+++ b/fs/proc/base.c
@@ -3187,6 +3187,7 @@ struct dentry *proc_pid_lookup(struct inode *dir, struct 
dentry * dentry, unsign
        unsigned tgid;
        struct proc_fs_info *fs_info = proc_sb(dir->i_sb);
        struct pid_namespace *ns = fs_info->pid_ns;
+       int limit_pids = proc_fs_limit_pids(fs_info);
 
        tgid = name_to_int(&dentry->d_name);
        if (tgid == ~0U)
@@ -3200,7 +3201,15 @@ struct dentry *proc_pid_lookup(struct inode *dir, struct 
dentry * dentry, unsign
        if (!task)
                goto out;
 
+       /* Limit procfs to only ptracable tasks */
+       if (limit_pids == PROC_LIMIT_PIDS_PTRACE) {
+               cond_resched();
+               if (!has_pid_permissions(fs_info, task, HIDEPID_NO_ACCESS))
+                       goto out_put_task;
+       }
+
        result = proc_pid_instantiate(dir, dentry, task, NULL);
+out_put_task:
        put_task_struct(task);
 out:
        return ERR_PTR(result);
-- 
2.10.5