[fuse-devel] fuse_get_context() and namespaces

Commit Message

Seth Forshee June 3, 2015, 2:03 p.m. UTC

On Mon, Jun 01, 2015 at 03:07:07PM +0200, Miklos Szeredi wrote:
> On Wed, May 27, 2015 at 2:55 PM, Seth Forshee
> <[e-mail]> wrote:
> 
> > I haven't seen anything to indicate that this filesystem will be broken
> > by this, just that it's broken by untranslated pids. Presumably it would
> > just reject any requests which aren't representable in its namespace.
> 
> Without failing the operation there never will be any indication that
> a filesystem is broken.  So I guess the safe way would be
> 
>  - deny access for untranslated pids (uids, gids, etc).
> 
>  - if this becomes an issue (possibly a perfomance issue), then add a
> flag to disable pids (and/or uids, gids) completely.

How about this then? I left fuse_get_req_nofail_nopages alone since it
presumably shouldn't fail, but that could be changed too.

With this pids are being translated into my container's namespace, and
access by processes whose pid won't map into the namespace is denied.

Seth

---

From 9fa40d5084b633902c781459fe853f9234e9f67c Mon Sep 17 00:00:00 2001
From: Seth Forshee <[e-mail]>
Date: Wed, 2 Jul 2014 16:29:19 -0500
Subject: [PATCH] fuse: Add support for pid namespaces

If the userspace process servicing fuse requests is running in
a pid namespace then pids passed via the fuse fd need to be
translated relative to that namespace. Capture the pid namespace
in use when the filesystem is mounted and use this for pid
translation.

Since no use case currently exists for changing namespaces all
translations are done relative to the pid namespace in use when
/dev/fuse is opened. Mounting or /dev/fuse IO from another
namespace will return errors.

Requests from processes whose pid cannot be translated into the
target namespace are not permitted, except for requests
allocated via fuse_get_req_nofail_nopages. For no-fail requests
in.h.pid will be 0 if the pid translation fails.

File locking changes based on previous work done by Eric
Biederman.

Signed-off-by: Seth Forshee <[e-mail]>
Signed-off-by: Miklos Szeredi <[e-mail]>
---
 fs/fuse/dev.c    | 19 +++++++++++++++----
 fs/fuse/file.c   | 22 +++++++++++++++++-----
 fs/fuse/fuse_i.h |  4 ++++
 fs/fuse/inode.c  |  3 +++
 4 files changed, 39 insertions(+), 9 deletions(-)


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Patch

diff --git a/fs/fuse/dev.c b/fs/fuse/dev.c
index 80cc1b35d460..b8b977dbdd8c 100644
--- a/fs/fuse/dev.c
+++ b/fs/fuse/dev.c
@@ -19,6 +19,7 @@ 
 #include <linux/pipe_fs_i.h>
 #include <linux/swap.h>
 #include <linux/splice.h>
+#include <linux/sched.h>
 
 MODULE_ALIAS_MISCDEV(FUSE_MINOR);
 MODULE_ALIAS("devname:fuse");
@@ -124,11 +125,11 @@  static void __fuse_put_request(struct fuse_req *req)
 	atomic_dec(&req->count);
 }
 
-static void fuse_req_init_context(struct fuse_req *req)
+static void fuse_req_init_context(struct fuse_conn *fc, struct fuse_req *req)
 {
 	req->in.h.uid = from_kuid_munged(&init_user_ns, current_fsuid());
 	req->in.h.gid = from_kgid_munged(&init_user_ns, current_fsgid());
-	req->in.h.pid = current->pid;
+	req->in.h.pid = pid_nr_ns(task_pid(current), fc->pid_ns);
 }
 
 void fuse_set_initialized(struct fuse_conn *fc)
@@ -181,10 +182,14 @@  static struct fuse_req *__fuse_get_req(struct fuse_conn *fc, unsigned npages,
 		goto out;
 	}
 
-	fuse_req_init_context(req);
+	fuse_req_init_context(fc, req);
 	__set_bit(FR_WAITING, &req->flags);
 	if (for_background)
 		__set_bit(FR_BACKGROUND, &req->flags);
+	if (req->in.h.pid == 0) {
+		fuse_put_request(fc, req);
+		return ERR_PTR(-EOVERFLOW);
+	}
 
 	return req;
 
@@ -274,7 +279,7 @@  struct fuse_req *fuse_get_req_nofail_nopages(struct fuse_conn *fc,
 	if (!req)
 		req = get_reserved_req(fc, file);
 
-	fuse_req_init_context(req);
+	fuse_req_init_context(fc, req);
 	__set_bit(FR_WAITING, &req->flags);
 	__clear_bit(FR_BACKGROUND, &req->flags);
 	return req;
@@ -1243,6 +1248,9 @@  static ssize_t fuse_dev_do_read(struct fuse_dev *fud, struct file *file,
 	struct fuse_in *in;
 	unsigned reqsize;
 
+	if (task_active_pid_ns(current) != fc->pid_ns)
+		return -EIO;
+
  restart:
 	spin_lock(&fiq->waitq.lock);
 	err = -EAGAIN;
@@ -1872,6 +1880,9 @@  static ssize_t fuse_dev_do_write(struct fuse_dev *fud,
 	struct fuse_req *req;
 	struct fuse_out_header oh;
 
+	if (task_active_pid_ns(current) != fc->pid_ns)
+		return -EIO;
+
 	if (nbytes < sizeof(struct fuse_out_header))
 		return -EINVAL;
 
diff --git a/fs/fuse/file.c b/fs/fuse/file.c
index 64835cf58936..3088bf360003 100644
--- a/fs/fuse/file.c
+++ b/fs/fuse/file.c
@@ -2061,7 +2061,8 @@  static int fuse_direct_mmap(struct file *file, struct vm_area_struct *vma)
 	return generic_file_mmap(file, vma);
 }
 
-static int convert_fuse_file_lock(const struct fuse_file_lock *ffl,
+static int convert_fuse_file_lock(struct fuse_conn *fc,
+				  const struct fuse_file_lock *ffl,
 				  struct file_lock *fl)
 {
 	switch (ffl->type) {
@@ -2076,7 +2077,14 @@  static int convert_fuse_file_lock(const struct fuse_file_lock *ffl,
 
 		fl->fl_start = ffl->start;
 		fl->fl_end = ffl->end;
-		fl->fl_pid = ffl->pid;
+
+		/*
+		 * Convert pid into the caller's pid namespace. If the pid
+		 * does not map into the namespace fl_pid will get set to 0.
+		 */
+		rcu_read_lock();
+		fl->fl_pid = pid_vnr(find_pid_ns(ffl->pid, fc->pid_ns));
+		rcu_read_unlock();
 		break;
 
 	default:
@@ -2125,7 +2133,7 @@  static int fuse_getlk(struct file *file, struct file_lock *fl)
 	args.out.args[0].value = &outarg;
 	err = fuse_simple_request(fc, &args);
 	if (!err)
-		err = convert_fuse_file_lock(&outarg.lk, fl);
+		err = convert_fuse_file_lock(fc, &outarg.lk, fl);
 
 	return err;
 }
@@ -2137,7 +2145,8 @@  static int fuse_setlk(struct file *file, struct file_lock *fl, int flock)
 	FUSE_ARGS(args);
 	struct fuse_lk_in inarg;
 	int opcode = (fl->fl_flags & FL_SLEEP) ? FUSE_SETLKW : FUSE_SETLK;
-	pid_t pid = fl->fl_type != F_UNLCK ? current->tgid : 0;
+	struct pid *pid = fl->fl_type != F_UNLCK ? task_tgid(current) : NULL;
+	pid_t pid_nr = pid_nr_ns(pid, fc->pid_ns);
 	int err;
 
 	if (fl->fl_lmops && fl->fl_lmops->lm_grant) {
@@ -2149,7 +2158,10 @@  static int fuse_setlk(struct file *file, struct file_lock *fl, int flock)
 	if (fl->fl_flags & FL_CLOSE)
 		return 0;
 
-	fuse_lk_fill(&args, file, fl, opcode, pid, flock, &inarg);
+	if (pid && pid_nr == 0)
+		return -EOVERFLOW;
+
+	fuse_lk_fill(&args, file, fl, opcode, pid_nr, flock, &inarg);
 	err = fuse_simple_request(fc, &args);
 
 	/* locking is restartable */
diff --git a/fs/fuse/fuse_i.h b/fs/fuse/fuse_i.h
index 405113101db8..143b595197b6 100644
--- a/fs/fuse/fuse_i.h
+++ b/fs/fuse/fuse_i.h
@@ -22,6 +22,7 @@ 
 #include <linux/rbtree.h>
 #include <linux/poll.h>
 #include <linux/workqueue.h>
+#include <linux/pid_namespace.h>
 
 /** Max number of pages that can be used in a single read request */
 #define FUSE_MAX_PAGES_PER_REQ 32
@@ -456,6 +457,9 @@  struct fuse_conn {
 	/** The group id for this mount */
 	kgid_t group_id;
 
+	/** The pid namespace for this mount */
+	struct pid_namespace *pid_ns;
+
 	/** The fuse mount flags for this mount */
 	unsigned flags;
 
diff --git a/fs/fuse/inode.c b/fs/fuse/inode.c
index ac81f48ab2f4..4a03ac733be9 100644
--- a/fs/fuse/inode.c
+++ b/fs/fuse/inode.c
@@ -20,6 +20,7 @@ 
 #include <linux/random.h>
 #include <linux/sched.h>
 #include <linux/exportfs.h>
+#include <linux/pid_namespace.h>
 
 MODULE_AUTHOR("Miklos Szeredi <[e-mail]>");
 MODULE_DESCRIPTION("Filesystem in Userspace");
@@ -609,6 +610,7 @@  void fuse_conn_init(struct fuse_conn *fc)
 	fc->connected = 1;
 	fc->attr_version = 1;
 	get_random_bytes(&fc->scramble_key, sizeof(fc->scramble_key));
+	fc->pid_ns = get_pid_ns(task_active_pid_ns(current));
 }
 EXPORT_SYMBOL_GPL(fuse_conn_init);
 
@@ -617,6 +619,7 @@  void fuse_conn_put(struct fuse_conn *fc)
 	if (atomic_dec_and_test(&fc->count)) {
 		if (fc->destroy_req)
 			fuse_request_free(fc->destroy_req);
+		put_pid_ns(fc->pid_ns);
 		fc->release(fc);
 	}
 }