File cve-2016-0728-check-reference-counts-for-overflow.patch of Package lttng-modules.8953
From: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Date: Tue Jan 19 09:51:55 2016 -0500
Subject: CVE-2016-0728 check reference counts for overflow
Git-commit: 4ce9f32b8ec6ff1de14d734607a5f4a20fb743e5
Signed-off-by: Tony Jones <tonyj@suse.de>
Fix: check reference counts for overflow
Linux kernel CVE-2016-0728 is a use-after-free based on overflow of the
reference counting mechanism.
Implement a kref wrapper in lttng that validates overflows, and use it
instead of kref_get(). Also check explicitly for overflows on file
fcount counters.
This should not be an issue in practice in lttng-modules because the ABI
is only exposed to root, but let's err on the safe side.
Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
diff --git a/lib/ringbuffer/ring_buffer_frontend.c b/lib/ringbuffer/ring_buffer_frontend.c
index c4b797c..dbe52c1 100644
--- a/lib/ringbuffer/ring_buffer_frontend.c
+++ b/lib/ringbuffer/ring_buffer_frontend.c
@@ -61,6 +61,7 @@
#include "../../wrapper/ringbuffer/iterator.h"
#include "../../wrapper/ringbuffer/nohz.h"
#include "../../wrapper/atomic.h"
+#include "../../wrapper/kref.h"
#include "../../wrapper/percpu-defs.h"
/*
@@ -793,7 +794,10 @@ int lib_ring_buffer_open_read(struct lib_ring_buffer *buf)
if (!atomic_long_add_unless(&buf->active_readers, 1, 1))
return -EBUSY;
- kref_get(&chan->ref);
+ if (!lttng_kref_get(&chan->ref)) {
+ atomic_long_dec(&buf->active_readers);
+ return -EOVERFLOW;
+ }
lttng_smp_mb__after_atomic();
return 0;
}
diff --git a/lttng-abi.c b/lttng-abi.c
index 3572e58..b51434a 100644
--- a/lttng-abi.c
+++ b/lttng-abi.c
@@ -50,6 +50,7 @@
#include "wrapper/ringbuffer/frontend.h"
#include "wrapper/poll.h"
#include "wrapper/file.h"
+#include "wrapper/kref.h"
#include "lttng-abi.h"
#include "lttng-abi-old.h"
#include "lttng-events.h"
@@ -417,6 +418,10 @@ int lttng_abi_create_channel(struct file *session_file,
transport_name = "<unknown>";
break;
}
+ if (atomic_long_add_unless(&session_file->f_count,
+ 1, INT_MAX) == INT_MAX) {
+ goto refcount_error;
+ }
/*
* We tolerate no failure path after channel creation. It will stay
* invariant for the rest of the session.
@@ -434,11 +439,12 @@ int lttng_abi_create_channel(struct file *session_file,
chan->file = chan_file;
chan_file->private_data = chan;
fd_install(chan_fd, chan_file);
- atomic_long_inc(&session_file->f_count);
return chan_fd;
chan_error:
+ atomic_long_dec(&session_file->f_count);
+refcount_error:
fput(chan_file);
file_error:
put_unused_fd(chan_fd);
@@ -927,17 +933,20 @@ int lttng_abi_open_metadata_stream(struct file *channel_file)
goto notransport;
}
+ if (!lttng_kref_get(&session->metadata_cache->refcount))
+ goto kref_error;
ret = lttng_abi_create_stream_fd(channel_file, stream_priv,
<tng_metadata_ring_buffer_file_operations);
if (ret < 0)
goto fd_error;
- kref_get(&session->metadata_cache->refcount);
list_add(&metadata_stream->list,
&session->metadata_cache->metadata_stream);
return ret;
fd_error:
+ kref_put(&session->metadata_cache->refcount, metadata_cache_destroy);
+kref_error:
module_put(metadata_stream->transport->owner);
notransport:
kfree(metadata_stream);
@@ -981,6 +990,11 @@ int lttng_abi_create_event(struct file *channel_file,
ret = PTR_ERR(event_file);
goto file_error;
}
+ /* The event holds a reference on the channel */
+ if (atomic_long_add_unless(&channel_file->f_count,
+ 1, INT_MAX) == INT_MAX) {
+ goto refcount_error;
+ }
if (event_param->instrumentation == LTTNG_KERNEL_TRACEPOINT
|| event_param->instrumentation == LTTNG_KERNEL_SYSCALL) {
struct lttng_enabler *enabler;
@@ -1012,11 +1026,11 @@ int lttng_abi_create_event(struct file *channel_file,
}
event_file->private_data = priv;
fd_install(event_fd, event_file);
- /* The event holds a reference on the channel */
- atomic_long_inc(&channel_file->f_count);
return event_fd;
event_error:
+ atomic_long_dec(&channel_file->f_count);
+refcount_error:
fput(event_file);
file_error:
put_unused_fd(event_fd);
diff --git a/lttng-events.c b/lttng-events.c
index 4b76ea0..d0ebb29 100644
--- a/lttng-events.c
+++ b/lttng-events.c
@@ -1043,17 +1043,22 @@ int lttng_session_list_tracker_pids(struct lttng_session *session)
ret = PTR_ERR(tracker_pids_list_file);
goto file_error;
}
+ if (atomic_long_add_unless(&session->file->f_count,
+ 1, INT_MAX) == INT_MAX) {
+ goto refcount_error;
+ }
ret = lttng_tracker_pids_list_fops.open(NULL, tracker_pids_list_file);
if (ret < 0)
goto open_error;
m = tracker_pids_list_file->private_data;
m->private = session;
fd_install(file_fd, tracker_pids_list_file);
- atomic_long_inc(&session->file->f_count);
return file_fd;
open_error:
+ atomic_long_dec(&session->file->f_count);
+refcount_error:
fput(tracker_pids_list_file);
file_error:
put_unused_fd(file_fd);
diff --git a/probes/lttng-kretprobes.c b/probes/lttng-kretprobes.c
index 52b3f78..10bb52f 100644
--- a/probes/lttng-kretprobes.c
+++ b/probes/lttng-kretprobes.c
@@ -219,9 +219,9 @@ int lttng_kretprobes_register(const char *name,
* unregistered. Same for memory allocation.
*/
kref_init(<tng_krp->kref_alloc);
- kref_get(<tng_krp->kref_alloc); /* inc refcount to 2 */
+ kref_get(<tng_krp->kref_alloc); /* inc refcount to 2, no overflow. */
kref_init(<tng_krp->kref_register);
- kref_get(<tng_krp->kref_register); /* inc refcount to 2 */
+ kref_get(<tng_krp->kref_register); /* inc refcount to 2, no overflow. */
/*
* Ensure the memory we just allocated don't trigger page faults.
diff --git a/wrapper/kref.h b/wrapper/kref.h
new file mode 100644
index 0000000..eedefbf
--- /dev/null
+++ b/wrapper/kref.h
@@ -0,0 +1,46 @@
+#ifndef _LTTNG_WRAPPER_KREF_H
+#define _LTTNG_WRAPPER_KREF_H
+
+/*
+ * wrapper/kref.h
+ *
+ * wrapper around linux/kref.h.
+ *
+ * Copyright (C) 2016 Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; only version 2 of the License.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License along
+ * with this program; if not, write to the Free Software Foundation, Inc.,
+ * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
+ *
+ * This wrapper code is derived from Linux 3.19.2 include/linux/list.h
+ * and include/linux/rculist.h, hence the GPLv2 license applied to this
+ * file.
+ */
+
+#include <linux/kref.h>
+#include <linux/rculist.h>
+
+/*
+ * lttng_kref_get: get reference count, checking for overflow.
+ *
+ * Return 1 if reference is taken, 0 otherwise (overflow).
+ */
+static inline int lttng_kref_get(struct kref *kref)
+{
+ if (atomic_add_unless(&kref->refcount, 1, INT_MAX) != INT_MAX) {
+ return 1;
+ } else {
+ return 0;
+ }
+}
+
+#endif /* _LTTNG_WRAPPER_KREF_H */
