From cc0f994c205df817b9ed4a29fd712fa0da82c68b Mon Sep 17 00:00:00 2001 From: Amir Goldstein Date: Tue, 25 Apr 2017 14:29:35 +0300 Subject: fanotify: don't expose EOPENSTALE to userspace commit 4ff33aafd32e084f5ee7faa54ba06e95f8b1b8af upstream. When delivering an event to userspace for a file on an NFS share, if the file is deleted on server side before user reads the event, user will not get the event. If the event queue contained several events, the stale event is quietly dropped and read() returns to user with events read so far in the buffer. If the event queue contains a single stale event or if the stale event is a permission event, read() returns to user with the kernel internal error code 518 (EOPENSTALE), which is not a POSIX error code. Check the internal return value -EOPENSTALE in fanotify_read(), just the same as it is checked in path_openat() and drop the event in the cases that it is not already dropped. This is a reproducer from Marko Rauhamaa: Just take the example program listed under "man fanotify" ("fantest") and follow these steps: ============================================================== NFS Server NFS Client(1) NFS Client(2) ============================================================== # echo foo >/nfsshare/bar.txt # cat /nfsshare/bar.txt foo # ./fantest /nfsshare Press enter key to terminate. Listening for events. # rm -f /nfsshare/bar.txt # cat /nfsshare/bar.txt read: Unknown error 518 cat: /nfsshare/bar.txt: Operation not permitted ============================================================== where NFS Client (1) and (2) are two terminal sessions on a single NFS Client machine. Reported-by: Marko Rauhamaa Tested-by: Marko Rauhamaa Cc: Signed-off-by: Amir Goldstein Signed-off-by: Jan Kara Signed-off-by: Greg Kroah-Hartman --- fs/notify/fanotify/fanotify_user.c | 26 ++++++++++++++++++-------- 1 file changed, 18 insertions(+), 8 deletions(-) (limited to 'fs/notify') diff --git a/fs/notify/fanotify/fanotify_user.c b/fs/notify/fanotify/fanotify_user.c index 7ebfca6a1427..258e8f635148 100644 --- a/fs/notify/fanotify/fanotify_user.c +++ b/fs/notify/fanotify/fanotify_user.c @@ -294,27 +294,37 @@ static ssize_t fanotify_read(struct file *file, char __user *buf, } ret = copy_event_to_user(group, kevent, buf); + if (unlikely(ret == -EOPENSTALE)) { + /* + * We cannot report events with stale fd so drop it. + * Setting ret to 0 will continue the event loop and + * do the right thing if there are no more events to + * read (i.e. return bytes read, -EAGAIN or wait). + */ + ret = 0; + } + /* * Permission events get queued to wait for response. Other * events can be destroyed now. */ if (!(kevent->mask & FAN_ALL_PERM_EVENTS)) { fsnotify_destroy_event(group, kevent); - if (ret < 0) - break; } else { #ifdef CONFIG_FANOTIFY_ACCESS_PERMISSIONS - if (ret < 0) { + if (ret <= 0) { FANOTIFY_PE(kevent)->response = FAN_DENY; wake_up(&group->fanotify_data.access_waitq); - break; + } else { + spin_lock(&group->notification_lock); + list_add_tail(&kevent->list, + &group->fanotify_data.access_list); + spin_unlock(&group->notification_lock); } - spin_lock(&group->notification_lock); - list_add_tail(&kevent->list, - &group->fanotify_data.access_list); - spin_unlock(&group->notification_lock); #endif } + if (ret < 0) + break; buf += ret; count -= ret; } -- cgit v1.2.3