[4.2.y-ckt stable] Patch "ebpf: fix fd refcount leaks related to maps in bpf syscall" has been added to staging queue

[Kamal Mostafa]

This is a note to let you know that I have just added a patch titled

    ebpf: fix fd refcount leaks related to maps in bpf syscall

to the linux-4.2.y-queue branch of the 4.2.y-ckt extended stable tree 
which can be found at:

    http://kernel.ubuntu.com/git/ubuntu/linux.git/log/?h=linux-4.2.y-queue

This patch is scheduled to be released in version 4.2.8-ckt1.

If you, or anyone else, feels it should not be added to this tree, please 
reply to this email.

For more information about the 4.2.y-ckt tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Kamal

------

>From 58789ced83d8743263bfd3d7cfecda0f4e76b574 Mon Sep 17 00:00:00 2001
From: Daniel Borkmann <daniel at iogearbox.net>
Date: Tue, 8 Sep 2015 18:00:09 +0200
Subject: ebpf: fix fd refcount leaks related to maps in bpf syscall

commit 592867bfabe2fcb449393ba7eb0de4f972a08c63 upstream.

We may already have gotten a proper fd struct through fdget(), so
whenever we return at the end of an map operation, we need to call
fdput(). However, each map operation from syscall side first probes
CHECK_ATTR() to verify that unused fields in the bpf_attr union are
zero.

In case of malformed input, we return with error, but the lookup to
the map_fd was already performed at that time, so that we return
without an corresponding fdput(). Fix it by performing an fdget()
only right before bpf_map_get(). The fdget() invocation on maps in
the verifier is not affected.

Fixes: db20fd2b0108 ("bpf: add lookup/update/delete/iterate methods to BPF maps")
Signed-off-by: Daniel Borkmann <daniel at iogearbox.net>
Acked-by: Alexei Starovoitov <ast at plumgrid.com>
Signed-off-by: David S. Miller <davem at davemloft.net>
Signed-off-by: Kamal Mostafa <kamal at canonical.com>
---
 kernel/bpf/syscall.c | 12 ++++++++----
 1 file changed, 8 insertions(+), 4 deletions(-)

diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
index a1b14d1..57d4f28 100644
--- a/kernel/bpf/syscall.c
+++ b/kernel/bpf/syscall.c
@@ -155,14 +155,15 @@ static int map_lookup_elem(union bpf_attr *attr)
 	void __user *ukey = u64_to_ptr(attr->key);
 	void __user *uvalue = u64_to_ptr(attr->value);
 	int ufd = attr->map_fd;
-	struct fd f = fdget(ufd);
 	struct bpf_map *map;
 	void *key, *value, *ptr;
+	struct fd f;
 	int err;

 	if (CHECK_ATTR(BPF_MAP_LOOKUP_ELEM))
 		return -EINVAL;

+	f = fdget(ufd);
 	map = bpf_map_get(f);
 	if (IS_ERR(map))
 		return PTR_ERR(map);
@@ -213,14 +214,15 @@ static int map_update_elem(union bpf_attr *attr)
 	void __user *ukey = u64_to_ptr(attr->key);
 	void __user *uvalue = u64_to_ptr(attr->value);
 	int ufd = attr->map_fd;
-	struct fd f = fdget(ufd);
 	struct bpf_map *map;
 	void *key, *value;
+	struct fd f;
 	int err;

 	if (CHECK_ATTR(BPF_MAP_UPDATE_ELEM))
 		return -EINVAL;

+	f = fdget(ufd);
 	map = bpf_map_get(f);
 	if (IS_ERR(map))
 		return PTR_ERR(map);
@@ -265,14 +267,15 @@ static int map_delete_elem(union bpf_attr *attr)
 {
 	void __user *ukey = u64_to_ptr(attr->key);
 	int ufd = attr->map_fd;
-	struct fd f = fdget(ufd);
 	struct bpf_map *map;
+	struct fd f;
 	void *key;
 	int err;

 	if (CHECK_ATTR(BPF_MAP_DELETE_ELEM))
 		return -EINVAL;

+	f = fdget(ufd);
 	map = bpf_map_get(f);
 	if (IS_ERR(map))
 		return PTR_ERR(map);
@@ -305,14 +308,15 @@ static int map_get_next_key(union bpf_attr *attr)
 	void __user *ukey = u64_to_ptr(attr->key);
 	void __user *unext_key = u64_to_ptr(attr->next_key);
 	int ufd = attr->map_fd;
-	struct fd f = fdget(ufd);
 	struct bpf_map *map;
 	void *key, *next_key;
+	struct fd f;
 	int err;

 	if (CHECK_ATTR(BPF_MAP_GET_NEXT_KEY))
 		return -EINVAL;

+	f = fdget(ufd);
 	map = bpf_map_get(f);
 	if (IS_ERR(map))
 		return PTR_ERR(map);
--
1.9.1