fuse: return -ECONNABORTED on /dev/fuse read after abort

Currently the userspace has no way of knowing whether the fuse
connection ended because of umount or abort via sysfs. It makes it hard
for filesystems to free the mountpoint after abort without worrying
about removing some new mount.

The patch fixes it by returning different errors when userspace reads
from /dev/fuse (-ENODEV for umount and -ECONNABORTED for abort).

Add a new capability flag FUSE_ABORT_ERROR. If set and the connection is
gone because of sysfs abort, reading from the device will return
-ECONNABORTED.

Signed-off-by: Szymon Lukasz <noh4hss@gmail.com>
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>

6 files changed, 29 insertions, 13 deletions

diff --git a/fs/fuse/control.c b/fs/fuse/control.c
index b9ea99c5b5b3..78fb7a07c5ca 100644
--- a/fs/fuse/control.c
+++ b/fs/fuse/control.c
@@ -35,7 +35,7 @@ static ssize_t fuse_conn_abort_write(struct file *file, const char __user *buf,
 {
         struct fuse_conn *fc = fuse_ctl_file_conn_get(file);
         if (fc) {
-                fuse_abort_conn(fc);
+                fuse_abort_conn(fc, true);
                 fuse_conn_put(fc);
         }
         return count;
diff --git a/fs/fuse/cuse.c b/fs/fuse/cuse.c
index e9e97803442a..31d33b69957f 100644
--- a/fs/fuse/cuse.c
+++ b/fs/fuse/cuse.c
@@ -406,7 +406,7 @@ err_unlock:
 err_region:
         unregister_chrdev_region(devt, 1);
 err:
-        fuse_abort_conn(fc);
+        fuse_abort_conn(fc, false);
         goto out;
 }
 
@@ -581,7 +581,7 @@ static ssize_t cuse_class_abort_store(struct device *dev,
 {
         struct cuse_conn *cc = dev_get_drvdata(dev);
 
-        fuse_abort_conn(&cc->fc);
+        fuse_abort_conn(&cc->fc, false);
         return count;
 }
 static DEVICE_ATTR(abort, 0200, NULL, cuse_class_abort_store);
diff --git a/fs/fuse/dev.c b/fs/fuse/dev.c
index 5d06384c2cae..78b6293bd04d 100644
--- a/fs/fuse/dev.c
+++ b/fs/fuse/dev.c
@@ -1234,9 +1234,10 @@ static ssize_t fuse_dev_do_read(struct fuse_dev *fud, struct file *file,
         if (err)
                 goto err_unlock;
 
-        err = -ENODEV;
-        if (!fiq->connected)
+        if (!fiq->connected) {
+                err = (fc->aborted && fc->abort_err) ? -ECONNABORTED : -ENODEV;
                 goto err_unlock;
+        }
 
         if (!list_empty(&fiq->interrupts)) {
                 req = list_entry(fiq->interrupts.next, struct fuse_req,
@@ -1287,7 +1288,7 @@ static ssize_t fuse_dev_do_read(struct fuse_dev *fud, struct file *file,
         spin_lock(&fpq->lock);
         clear_bit(FR_LOCKED, &req->flags);
         if (!fpq->connected) {
-                err = -ENODEV;
+                err = (fc->aborted && fc->abort_err) ? -ECONNABORTED : -ENODEV;
                 goto out_end;
         }
         if (err) {
@@ -2076,7 +2077,7 @@ static void end_polls(struct fuse_conn *fc)
  * is OK, the request will in that case be removed from the list before we touch
  * it.
  */
-void fuse_abort_conn(struct fuse_conn *fc)
+void fuse_abort_conn(struct fuse_conn *fc, bool is_abort)
 {
         struct fuse_iqueue *fiq = &fc->iq;
 
@@ -2089,6 +2090,7 @@ void fuse_abort_conn(struct fuse_conn *fc)
 
                 fc->connected = 0;
                 fc->blocked = 0;
+                fc->aborted = is_abort;
                 fuse_set_initialized(fc);
                 list_for_each_entry(fud, &fc->devices, entry) {
                         struct fuse_pqueue *fpq = &fud->pq;
@@ -2151,7 +2153,7 @@ int fuse_dev_release(struct inode *inode, struct file *file)
                 /* Are we the last open device? */
                 if (atomic_dec_and_test(&fc->dev_count)) {
                         WARN_ON(fc->iq.fasync != NULL);
-                        fuse_abort_conn(fc);
+                        fuse_abort_conn(fc, false);
                 }
                 fuse_dev_free(fud);
         }
diff --git a/fs/fuse/fuse_i.h b/fs/fuse/fuse_i.h
index c4c093bbf456..7d2e7deea64b 100644
--- a/fs/fuse/fuse_i.h
+++ b/fs/fuse/fuse_i.h
@@ -515,6 +515,9 @@ struct fuse_conn {
             abort and device release */
         unsigned connected;
 
+        /** Connection aborted via sysfs */
+        bool aborted;
+
         /** Connection failed (version mismatch).  Cannot race with
             setting other bitfields since it is only set once in INIT
             reply, before any other request, and never cleared */
@@ -526,6 +529,9 @@ struct fuse_conn {
         /** Do readpages asynchronously?  Only set in INIT */
         unsigned async_read:1;
 
+        /** Return an unique read error after abort.  Only set in INIT */
+        unsigned abort_err:1;
+
         /** Do not send separate SETATTR request before open(O_TRUNC)  */
         unsigned atomic_o_trunc:1;
 
@@ -851,7 +857,7 @@ void fuse_request_send_background_locked(struct fuse_conn *fc,
                                          struct fuse_req *req);
 
 /* Abort all requests */
-void fuse_abort_conn(struct fuse_conn *fc);
+void fuse_abort_conn(struct fuse_conn *fc, bool is_abort);
 
 /**
  * Invalidate inode attributes
diff --git a/fs/fuse/inode.c b/fs/fuse/inode.c
index 624f18bbfd2b..3c9b675d99da 100644
--- a/fs/fuse/inode.c
+++ b/fs/fuse/inode.c
@@ -371,7 +371,7 @@ void fuse_unlock_inode(struct inode *inode)
 
 static void fuse_umount_begin(struct super_block *sb)
 {
-        fuse_abort_conn(get_fuse_conn_super(sb));
+        fuse_abort_conn(get_fuse_conn_super(sb), false);
 }
 
 static void fuse_send_destroy(struct fuse_conn *fc)
@@ -393,7 +393,7 @@ static void fuse_put_super(struct super_block *sb)
 
         fuse_send_destroy(fc);
 
-        fuse_abort_conn(fc);
+        fuse_abort_conn(fc, false);
         mutex_lock(&fuse_mutex);
         list_del(&fc->entry);
         fuse_ctl_remove_conn(fc);
@@ -918,6 +918,8 @@ static void process_init_reply(struct fuse_conn *fc, struct fuse_req *req)
                                 fc->posix_acl = 1;
                                 fc->sb->s_xattr = fuse_acl_xattr_handlers;
                         }
+                        if (arg->flags & FUSE_ABORT_ERROR)
+                                fc->abort_err = 1;
                 } else {
                         ra_pages = fc->max_read / PAGE_SIZE;
                         fc->no_lock = 1;
@@ -948,7 +950,8 @@ static void fuse_send_init(struct fuse_conn *fc, struct fuse_req *req)
                 FUSE_FLOCK_LOCKS | FUSE_HAS_IOCTL_DIR | FUSE_AUTO_INVAL_DATA |
                 FUSE_DO_READDIRPLUS | FUSE_READDIRPLUS_AUTO | FUSE_ASYNC_DIO |
                 FUSE_WRITEBACK_CACHE | FUSE_NO_OPEN_SUPPORT |
-                FUSE_PARALLEL_DIROPS | FUSE_HANDLE_KILLPRIV | FUSE_POSIX_ACL;
+                FUSE_PARALLEL_DIROPS | FUSE_HANDLE_KILLPRIV | FUSE_POSIX_ACL |
+                FUSE_ABORT_ERROR;
         req->in.h.opcode = FUSE_INIT;
         req->in.numargs = 1;
         req->in.args[0].size = sizeof(*arg);
diff --git a/include/uapi/linux/fuse.h b/include/uapi/linux/fuse.h
index 4b5001c57f46..92fa24c24c92 100644
--- a/include/uapi/linux/fuse.h
+++ b/include/uapi/linux/fuse.h
@@ -113,6 +113,9 @@
  *  7.26
  *  - add FUSE_HANDLE_KILLPRIV
  *  - add FUSE_POSIX_ACL
+ *
+ *  7.27
+ *  - add FUSE_ABORT_ERROR
  */
 
 #ifndef _LINUX_FUSE_H
@@ -148,7 +151,7 @@
 #define FUSE_KERNEL_VERSION 7
 
 /** Minor version number of this interface */