Merge branch 'bpfilter'

Alexei Starovoitov says:

====================
bpfilter

v2->v3:
- followed Luis's suggestion and significantly simplied first patch
  with shmem_kernel_file_setup+kernel_write. Added kdoc for new helper
- fixed typos and race to access pipes with mutex
- tested with bpfilter being 'builtin'. CONFIG_BPFILTER_UMH=y|m both work.
  Interesting to see a usermode executable being embedded inside vmlinux.
- it doesn't hurt to enable bpfilter in .config.
  ip_setsockopt commands sent to usermode via pipes and -ENOPROTOOPT is
  returned from userspace, so kernel falls back to original iptables code

v1->v2:
this patch set is almost a full rewrite of the earlier umh modules approach
The v1 of patches and follow up discussion was covered by LWN:
https://lwn.net/Articles/749108/

I believe the v2 addresses all issues brought up by Andy and others.
Mainly there are zero changes to kernel/module.c
Instead of teaching module loading logic to recognize special
umh module, let normal kernel modules execute part of its own
.init.rodata as a new user space process (Andy's idea)
Patch 1 introduces this new helper:
int fork_usermode_blob(void *data, size_t len, struct umh_info *info);
Input:
  data + len == executable file
Output:
  struct umh_info {
       struct file *pipe_to_umh;
       struct file *pipe_from_umh;
       pid_t pid;
  };

Advantages vs v1:
- the embedded user mode executable is stored as .init.rodata inside
  normal kernel module. These pages are freed when .ko finishes loading
- the elf file is copied into tmpfs file. The user mode process is swappable.
- the communication between user mode process and 'parent' kernel module
  is done via two unix pipes, hence protocol is not exposed to
  user space
- impossible to launch umh on its own (that was the main issue of v1)
  and impossible to be man-in-the-middle due to pipes
- bpfilter.ko consists of tiny kernel part that passes the data
  between kernel and umh via pipes and much bigger umh part that
  doing all the work
- 'lsmod' shows bpfilter.ko as usual.
  'rmmod bpfilter' removes kernel module and kills corresponding umh
- signed bpfilter.ko covers the whole image including umh code

Few issues:
- the user can still attach to the process and debug it with
  'gdb /proc/pid/exe pid', but 'gdb -p pid' doesn't work.
  (a bit worse comparing to v1)
- tinyconfig will notice a small increase in .text
  +766 | TEXT | 7c8b94806bec umh: introduce fork_usermode_blob() helper
====================

Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 122 insertions, 3 deletions

diff --git a/kernel/umh.c b/kernel/umh.c
index f76b3ff876cf..30db93fd7e39 100644
--- a/kernel/umh.c
+++ b/kernel/umh.c
@@ -25,6 +25,8 @@
 #include <linux/ptrace.h>
 #include <linux/async.h>
 #include <linux/uaccess.h>
+#include <linux/shmem_fs.h>
+#include <linux/pipe_fs_i.h>
 
 #include <trace/events/module.h>
 
@@ -97,9 +99,13 @@ static int call_usermodehelper_exec_async(void *data)
 
 	commit_creds(new);
 
-	retval = do_execve(getname_kernel(sub_info->path),
-			   (const char __user *const __user *)sub_info->argv,
-			   (const char __user *const __user *)sub_info->envp);
+	if (sub_info->file)
+		retval = do_execve_file(sub_info->file,
+					sub_info->argv, sub_info->envp);
+	else
+		retval = do_execve(getname_kernel(sub_info->path),
+				   (const char __user *const __user *)sub_info->argv,
+				   (const char __user *const __user *)sub_info->envp);
 out:
 	sub_info->retval = retval;
 	/*
@@ -185,6 +191,8 @@ static void call_usermodehelper_exec_work(struct work_struct *work)
 		if (pid < 0) {
 			sub_info->retval = pid;
 			umh_complete(sub_info);
+		} else {
+			sub_info->pid = pid;
 		}
 	}
 }
@@ -393,6 +401,117 @@ struct subprocess_info *call_usermodehelper_setup(const char *path, char **argv,
 }
 EXPORT_SYMBOL(call_usermodehelper_setup);
 
+struct subprocess_info *call_usermodehelper_setup_file(struct file *file,
+		int (*init)(struct subprocess_info *info, struct cred *new),
+		void (*cleanup)(struct subprocess_info *info), void *data)
+{
+	struct subprocess_info *sub_info;
+
+	sub_info = kzalloc(sizeof(struct subprocess_info), GFP_KERNEL);
+	if (!sub_info)
+		return NULL;
+
+	INIT_WORK(&sub_info->work, call_usermodehelper_exec_work);
+	sub_info->path = "none";
+	sub_info->file = file;
+	sub_info->init = init;
+	sub_info->cleanup = cleanup;
+	sub_info->data = data;
+	return sub_info;
+}
+
+static int umh_pipe_setup(struct subprocess_info *info, struct cred *new)
+{
+	struct umh_info *umh_info = info->data;
+	struct file *from_umh[2];
+	struct file *to_umh[2];
+	int err;
+
+	/* create pipe to send data to umh */
+	err = create_pipe_files(to_umh, 0);
+	if (err)
+		return err;
+	err = replace_fd(0, to_umh[0], 0);
+	fput(to_umh[0]);
+	if (err < 0) {
+		fput(to_umh[1]);
+		return err;
+	}
+
+	/* create pipe to receive data from umh */
+	err = create_pipe_files(from_umh, 0);
+	if (err) {
+		fput(to_umh[1]);
+		replace_fd(0, NULL, 0);
+		return err;
+	}
+	err = replace_fd(1, from_umh[1], 0);
+	fput(from_umh[1]);
+	if (err < 0) {
+		fput(to_umh[1]);
+		replace_fd(0, NULL, 0);
+		fput(from_umh[0]);
+		return err;
+	}
+
+	umh_info->pipe_to_umh = to_umh[1];
+	umh_info->pipe_from_umh = from_umh[0];
+	return 0;
+}
+
+static void umh_save_pid(struct subprocess_info *info)
+{
+	struct umh_info *umh_info = info->data;
+
+	umh_info->pid = info->pid;
+}
+
+/**
+ * fork_usermode_blob - fork a blob of bytes as a usermode process
+ * @data: a blob of bytes that can be do_execv-ed as a file
+ * @len: length of the blob
+ * @info: information about usermode process (shouldn't be NULL)
+ *
+ * Returns either negative error or zero which indicates success
+ * in executing a blob of bytes as a usermode process. In such
+ * case 'struct umh_info *info' is populated with two pipes
+ * and a pid of the process. The caller is responsible for health
+ * check of the user process, killing it via pid, and closing the
+ * pipes when user process is no longer needed.
+ */
+int fork_usermode_blob(void *data, size_t len, struct umh_info *info)
+{
+	struct subprocess_info *sub_info;
+	struct file *file;
+	ssize_t written;
+	loff_t pos = 0;
+	int err;
+
+	file = shmem_kernel_file_setup("", len, 0);
+	if (IS_ERR(file))
+		return PTR_ERR(file);
+
+	written = kernel_write(file, data, len, &pos);
+	if (written != len) {
+		err = written;
+		if (err >= 0)
+			err = -ENOMEM;
+		goto out;
+	}
+
+	err = -ENOMEM;
+	sub_info = call_usermodehelper_setup_file(file, umh_pipe_setup,
+						  umh_save_pid, info);
+	if (!sub_info)
+		goto out;
+
+	err = call_usermodehelper_exec(sub_info, UMH_WAIT_EXEC);
+out:
+	fput(file);
+	return err;
+}
+EXPORT_SYMBOL_GPL(fork_usermode_blob);
+
 /**
  * call_usermodehelper_exec - start a usermode application
  * @sub_info: information about the subprocessa