xsk: fix umem memory leak on cleanup

When the umem is cleaned up, the task that created it might already be
gone. If the task was gone, the xdp_umem_release function did not free
the pages member of struct xdp_umem.

It turned out that the task lookup was not needed at all; The code was
a left-over when we moved from task accounting to user accounting [1].

This patch fixes the memory leak by removing the task lookup logic
completely.

[1] https://lore.kernel.org/netdev/20180131135356.19134-3-bjorn.topel@gmail.com/

Link: https://lore.kernel.org/netdev/c1cb2ca8-6a14-3980-8672-f3de0bb38dfd@suse.cz/
Fixes: c0c77d8f ("xsk: add user memory registration support sockopt")
Reported-by: Jiri Slaby <jslaby@suse.cz>
Signed-off-by: Björn Töpel <bjorn.topel@intel.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>

include/net/xdp_sock.h

@@ -36,7 +36,6 @@ struct xdp_umem {
 	u32 headroom;
 	u32 chunk_size_nohr;
 	struct user_struct *user;
-	struct pid *pid;
 	unsigned long address;
 	refcount_t users;
 	struct work_struct work;

net/xdp/xdp_umem.c

@@ -193,9 +193,6 @@ static void xdp_umem_unaccount_pages(struct xdp_umem *umem)
 
 static void xdp_umem_release(struct xdp_umem *umem)
 {
-	struct task_struct *task;
-	struct mm_struct *mm;
-
 	xdp_umem_clear_dev(umem);
 
 	ida_simple_remove(&umem_ida, umem->id);
@@ -214,21 +211,10 @@ static void xdp_umem_release(struct xdp_umem *umem)
 
 	xdp_umem_unpin_pages(umem);
 
-	task = get_pid_task(umem->pid, PIDTYPE_PID);
-	put_pid(umem->pid);
-	if (!task)
-		goto out;
-	mm = get_task_mm(task);
-	put_task_struct(task);
-	if (!mm)
-		goto out;
-
-	mmput(mm);
 	kfree(umem->pages);
 	umem->pages = NULL;
 
 	xdp_umem_unaccount_pages(umem);
-out:
 	kfree(umem);
 }
 
@@ -357,7 +343,6 @@ static int xdp_umem_reg(struct xdp_umem *umem, struct xdp_umem_reg *mr)
 	if (size_chk < 0)
 		return -EINVAL;
 
-	umem->pid = get_task_pid(current, PIDTYPE_PID);
 	umem->address = (unsigned long)addr;
 	umem->chunk_mask = ~((u64)chunk_size - 1);
 	umem->size = size;
@@ -373,7 +358,7 @@ static int xdp_umem_reg(struct xdp_umem *umem, struct xdp_umem_reg *mr)
 
 	err = xdp_umem_account_pages(umem);
 	if (err)
-		goto out;
+		return err;
 
 	err = xdp_umem_pin_pages(umem);
 	if (err)
@@ -392,8 +377,6 @@ static int xdp_umem_reg(struct xdp_umem *umem, struct xdp_umem_reg *mr)
 
 out_account:
 	xdp_umem_unaccount_pages(umem);
-out:
-	put_pid(umem->pid);
 	return err;
 }