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.

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

Cc: Eric W. Biederman <ebiederm@xmission.com>
Cc: Serge H. Hallyn <serge.hallyn@ubuntu.com>
Cc: Andy Lutomirski <luto@amacapital.net>
Signed-off-by: Seth Forshee <seth.forshee@canonical.com>

fs/fuse/dev.c

@@ -20,6 +20,7 @@
 #include <linux/swap.h>
 #include <linux/splice.h>
 #include <linux/aio.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);
 }
 
 static bool fuse_block_alloc(struct fuse_conn *fc, bool for_background)
@@ -168,7 +169,7 @@ 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);
 	req->waiting = 1;
 	req->background = for_background;
 	return req;
@@ -257,7 +258,7 @@ 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);
 	req->waiting = 1;
 	req->background = 0;
 	return req;

fs/fuse/file.c

@@ -2131,7 +2131,8 @@ 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) {
@@ -2146,7 +2147,11 @@ 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;
+		rcu_read_lock();
+		fl->fl_pid = pid_vnr(find_pid_ns(ffl->pid, fc->pid_ns));
+		rcu_read_unlock();
+		if (ffl->pid != 0 && fl->fl_pid == 0)
+			return -EIO;
 		break;
 
 	default:
@@ -2156,9 +2161,9 @@ static int convert_fuse_file_lock(const struct fuse_file_lock *ffl,
 	return 0;
 }
 
-static void fuse_lk_fill(struct fuse_req *req, struct file *file,
-			 const struct file_lock *fl, int opcode, pid_t pid,
-			 int flock)
+static int fuse_lk_fill(struct fuse_req *req, struct file *file,
+			 const struct file_lock *fl, int opcode,
+			 struct pid *pid, int flock)
 {
 	struct inode *inode = file_inode(file);
 	struct fuse_conn *fc = get_fuse_conn(inode);
@@ -2170,7 +2175,9 @@ static void fuse_lk_fill(struct fuse_req *req, struct file *file,
 	arg->lk.start = fl->fl_start;
 	arg->lk.end = fl->fl_end;
 	arg->lk.type = fl->fl_type;
-	arg->lk.pid = pid;
+	arg->lk.pid = pid_nr_ns(pid, fc->pid_ns);
+	if (pid && arg->lk.pid == 0)
+		return -EOVERFLOW;
 	if (flock)
 		arg->lk_flags |= FUSE_LK_FLOCK;
 	req->in.h.opcode = opcode;
@@ -2178,6 +2185,8 @@ static void fuse_lk_fill(struct fuse_req *req, struct file *file,
 	req->in.numargs = 1;
 	req->in.args[0].size = sizeof(*arg);
 	req->in.args[0].value = arg;
+
+	return 0;
 }
 
 static int fuse_getlk(struct file *file, struct file_lock *fl)
@@ -2192,16 +2201,19 @@ static int fuse_getlk(struct file *file, struct file_lock *fl)
 	if (IS_ERR(req))
 		return PTR_ERR(req);
 
-	fuse_lk_fill(req, file, fl, FUSE_GETLK, 0, 0);
+	err = fuse_lk_fill(req, file, fl, FUSE_GETLK, NULL, 0);
+	if (err)
+		goto out;
 	req->out.numargs = 1;
 	req->out.args[0].size = sizeof(outarg);
 	req->out.args[0].value = &outarg;
 	fuse_request_send(fc, req);
 	err = req->out.h.error;
-	fuse_put_request(fc, req);
 	if (!err)
-		err = convert_fuse_file_lock(&outarg.lk, fl);
+		err = convert_fuse_file_lock(fc, &outarg.lk, fl);
 
+out:
+	fuse_put_request(fc, req);
 	return err;
 }
 
@@ -2211,7 +2223,7 @@ static int fuse_setlk(struct file *file, struct file_lock *fl, int flock)
 	struct fuse_conn *fc = get_fuse_conn(inode);
 	struct fuse_req *req;
 	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;
 	int err;
 
 	if (fl->fl_lmops && fl->fl_lmops->lm_grant) {
@@ -2227,12 +2239,16 @@ static int fuse_setlk(struct file *file, struct file_lock *fl, int flock)
 	if (IS_ERR(req))
 		return PTR_ERR(req);
 
-	fuse_lk_fill(req, file, fl, opcode, pid, flock);
+	err = fuse_lk_fill(req, file, fl, opcode, pid, flock);
+	if (err)
+		goto out;
 	fuse_request_send(fc, req);
 	err = req->out.h.error;
 	/* locking is restartable */
 	if (err == -EINTR)
 		err = -ERESTARTSYS;
+
+out:
 	fuse_put_request(fc, req);
 	return err;
 }

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
@@ -386,6 +387,9 @@ 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;
 

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 <miklos@szeredi.hu>");
 MODULE_DESCRIPTION("Filesystem in Userspace");
@@ -616,6 +617,7 @@ void fuse_conn_init(struct fuse_conn *fc)
 	fc->initialized = 0;
 	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);
 
@@ -624,6 +626,8 @@ 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->pid_ns = NULL;
 		fc->release(fc);
 	}
 }