Re: [PATCH net-next] nfnetlink_queue: enable PID info retrieval

On Fri, 2016-06-10 at 14:29 +0000, David Laight wrote:

From: Eric Dumazet

quoted

Sent: 09 June 2016 22:17
On Thu, 2016-06-09 at 23:50 +0300, Saeed Mahameed wrote:

quoted

From: Matthew Finlay <redacted>

quoted

diff --git a/net/socket.c b/net/socket.c
index a1bd161..67de200 100644
--- a/net/socket.c
+++ b/net/socket.c

@@ -382,6 +382,7 @@ struct file *sock_alloc_file(struct socket *sock, int flags, const char *dname)
 	}

 	sock->file = file;
+	file->f_owner.sock_pid  = find_get_pid(task_pid_nr(current));
 	file->f_flags = O_RDWR | (flags & O_NONBLOCK);
 	file->private_data = sock;
 	return file;

Wow, that is a serious memory leak weapon (of struct pid)

Why don't you store the pid value, instead of a pointer ?

Since the numeric 'pid' values can be reused (with no grace time) you'd
need to hold a reference to the pid structure (added in about 2.6.27) instead.
Which is just a smaller memory leak!

Smaller than what ?


I fail to see how keeping a reference on the pid structure of the
process who created a socket can be useful, other than some optional
LSM.

A socket can be given via af_unix to another process.

Original process might have died.

Keeping a ref on the pid wont prevent this.

So the 'pid' here looks as a pure hint/info. Better store it directly
and avoid all the ref counting and indirection games that are going to
slow down nfnetlink quite a lot with all these extra cache line misses
and locks.