[PATCH] proc: Proper pidns handling for /proc/self

[ebiederm@xmission.com (Eric W. Biederman)]

Currently if you access a /proc that is not mounted with your
processes current pid namespace /proc/self will point at a completely
different process.  Ouch!.

This patch fixes /proc/self to point to the current process if
it is available in the particular mount of /proc or to return
-ENOENT if the current process is not visible.

Signed-off-by: Eric W. Biederman <ebiederm@xmission.com>
---
 fs/proc/base.c |   12 ++++++++++--
 1 files changed, 10 insertions(+), 2 deletions(-)

diff --git a/fs/proc/base.c b/fs/proc/base.c
index 7e8eca4..34a1821 100644
--- a/fs/proc/base.c
+++ b/fs/proc/base.c
@@ -2049,15 +2049,23 @@ static const struct file_operations proc_coredump_filter_operations = {
 static int proc_self_readlink(struct dentry *dentry, char __user *buffer,
 			      int buflen)
 {
+	struct pid_namespace *ns = dentry->d_sb->s_fs_info;
+	pid_t tgid = task_tgid_nr_ns(current, ns);
 	char tmp[PROC_NUMBUF];
-	sprintf(tmp, "%d", task_tgid_vnr(current));
+	if (!tgid)
+		return -ENOENT;
+	sprintf(tmp, "%d", tgid);
 	return vfs_readlink(dentry,buffer,buflen,tmp);
 }
 
 static void *proc_self_follow_link(struct dentry *dentry, struct nameidata *nd)
 {
+	struct pid_namespace *ns = dentry->d_sb->s_fs_info;
+	pid_t tgid = task_tgid_nr_ns(current, ns);
 	char tmp[PROC_NUMBUF];
-	sprintf(tmp, "%d", task_tgid_vnr(current));
+	if (!tgid)
+		return ERR_PTR(-ENOENT);
+	sprintf(tmp, "%d", task_tgid_nr_ns(current, ns));
 	return ERR_PTR(vfs_follow_link(nd,tmp));
 }
 
-- 
1.5.3.rc6.17.g1911