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authorAmir Goldstein <amir73il@gmail.com>2021-03-04 13:29:21 +0200
committerJan Kara <jack@suse.cz>2021-03-16 16:55:05 +0100
commit7cea2a3c505e87a9d6afc78be4a7f7be636a73a7 (patch)
tree882cbff97b13a3f27259057d04be3bceff17e080 /fs/notify
parent5b8fea65d197f408bb00b251c70d842826d6b70b (diff)
downloadlinux-7cea2a3c505e87a9d6afc78be4a7f7be636a73a7.tar.bz2
fanotify: support limited functionality for unprivileged users
Add limited support for unprivileged fanotify groups. An unprivileged users is not allowed to get an open file descriptor in the event nor the process pid of another process. An unprivileged user cannot request permission events, cannot set mount/filesystem marks and cannot request unlimited queue/marks. This enables the limited functionality similar to inotify when watching a set of files and directories for OPEN/ACCESS/MODIFY/CLOSE events, without requiring SYS_CAP_ADMIN privileges. The FAN_REPORT_DFID_NAME init flag, provide a method for an unprivileged listener watching a set of directories (with FAN_EVENT_ON_CHILD) to monitor all changes inside those directories. This typically requires that the listener keeps a map of watched directory fid to dirfd (O_PATH), where fid is obtained with name_to_handle_at() before starting to watch for changes. When getting an event, the reported fid of the parent should be resolved to dirfd and fstatsat(2) with dirfd and name should be used to query the state of the filesystem entry. Link: https://lore.kernel.org/r/20210304112921.3996419-3-amir73il@gmail.com Signed-off-by: Amir Goldstein <amir73il@gmail.com> Signed-off-by: Jan Kara <jack@suse.cz>
Diffstat (limited to 'fs/notify')
-rw-r--r--fs/notify/fanotify/fanotify_user.c29
-rw-r--r--fs/notify/fdinfo.c3
2 files changed, 29 insertions, 3 deletions
diff --git a/fs/notify/fanotify/fanotify_user.c b/fs/notify/fanotify/fanotify_user.c
index e81848e09646..65142b1fa823 100644
--- a/fs/notify/fanotify/fanotify_user.c
+++ b/fs/notify/fanotify/fanotify_user.c
@@ -419,6 +419,14 @@ static ssize_t copy_event_to_user(struct fsnotify_group *group,
metadata.reserved = 0;
metadata.mask = event->mask & FANOTIFY_OUTGOING_EVENTS;
metadata.pid = pid_vnr(event->pid);
+ /*
+ * For an unprivileged listener, event->pid can be used to identify the
+ * events generated by the listener process itself, without disclosing
+ * the pids of other processes.
+ */
+ if (!capable(CAP_SYS_ADMIN) &&
+ task_tgid(current) != event->pid)
+ metadata.pid = 0;
if (path && path->mnt && path->dentry) {
fd = create_fd(group, path, &f);
@@ -1036,8 +1044,16 @@ SYSCALL_DEFINE2(fanotify_init, unsigned int, flags, unsigned int, event_f_flags)
pr_debug("%s: flags=%x event_f_flags=%x\n",
__func__, flags, event_f_flags);
- if (!capable(CAP_SYS_ADMIN))
- return -EPERM;
+ if (!capable(CAP_SYS_ADMIN)) {
+ /*
+ * An unprivileged user can setup an fanotify group with
+ * limited functionality - an unprivileged group is limited to
+ * notification events with file handles and it cannot use
+ * unlimited queue/marks.
+ */
+ if ((flags & FANOTIFY_ADMIN_INIT_FLAGS) || !fid_mode)
+ return -EPERM;
+ }
#ifdef CONFIG_AUDITSYSCALL
if (flags & ~(FANOTIFY_INIT_FLAGS | FAN_ENABLE_AUDIT))
@@ -1289,6 +1305,15 @@ static int do_fanotify_mark(int fanotify_fd, unsigned int flags, __u64 mask,
group = f.file->private_data;
/*
+ * An unprivileged user is not allowed to watch a mount point nor
+ * a filesystem.
+ */
+ ret = -EPERM;
+ if (!capable(CAP_SYS_ADMIN) &&
+ mark_type != FAN_MARK_INODE)
+ goto fput_and_out;
+
+ /*
* group->priority == FS_PRIO_0 == FAN_CLASS_NOTIF. These are not
* allowed to set permissions events.
*/
diff --git a/fs/notify/fdinfo.c b/fs/notify/fdinfo.c
index f0d6b54be412..a712b2aaa9ac 100644
--- a/fs/notify/fdinfo.c
+++ b/fs/notify/fdinfo.c
@@ -144,7 +144,8 @@ void fanotify_show_fdinfo(struct seq_file *m, struct file *f)
struct fsnotify_group *group = f->private_data;
seq_printf(m, "fanotify flags:%x event-flags:%x\n",
- group->fanotify_data.flags, group->fanotify_data.f_flags);
+ group->fanotify_data.flags,
+ group->fanotify_data.f_flags);
show_fdinfo(m, f, fanotify_fdinfo);
}