[PATCH 4.9 52/62] llc: fix sk_buff leak in llc_conn_service()

Greg Kroah-Hartman
2019-11-04T22:25:39Z

From: Eric Biggers <ebiggers@google.com>

commit b74555de21acd791f12c4a1aeaf653dd7ac21133 upstream.

syzbot reported:

BUG: memory leak
unreferenced object 0xffff88811eb3de00 (size 224):
comm "syz-executor559", pid 7315, jiffies 4294943019 (age 10.300s)
hex dump (first 32 bytes):
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
00 a0 38 24 81 88 ff ff 00 c0 f2 15 81 88 ff ff ..8$............
backtrace:
[<000000008d1c66a1>] kmemleak_alloc_recursive include/linux/kmemleak.h:55 [inline]
[<000000008d1c66a1>] slab_post_alloc_hook mm/slab.h:439 [inline]
[<000000008d1c66a1>] slab_alloc_node mm/slab.c:3269 [inline]
[<000000008d1c66a1>] kmem_cache_alloc_node+0x153/0x2a0 mm/slab.c:3579
[<00000000447d9496>] __alloc_skb+0x6e/0x210 net/core/skbuff.c:198
[<000000000cdbf82f>] alloc_skb include/linux/skbuff.h:1058 [inline]
[<000000000cdbf82f>] llc_alloc_frame+0x66/0x110 net/llc/llc_sap.c:54
[<000000002418b52e>] llc_conn_ac_send_sabme_cmd_p_set_x+0x2f/0x140 net/llc/llc_c_ac.c:777
[<000000001372ae17>] llc_exec_conn_trans_actions net/llc/llc_conn.c:475 [inline]
[<000000001372ae17>] llc_conn_service net/llc/llc_conn.c:400 [inline]
[<000000001372ae17>] llc_conn_state_process+0x1ac/0x640 net/llc/llc_conn.c:75
[<00000000f27e53c1>] llc_establish_connection+0x110/0x170 net/llc/llc_if.c:109
[<00000000291b2ca0>] llc_ui_connect+0x10e/0x370 net/llc/af_llc.c:477
[<000000000f9c740b>] __sys_connect+0x11d/0x170 net/socket.c:1840
[...]

The bug is that most callers of llc_conn_send_pdu() assume it consumes a
reference to the skb, when actually due to commit b85ab56c3f81 ("llc:
properly handle dev_queue_xmit() return value") it doesn't.

Revert most of that commit, and instead make the few places that need
llc_conn_send_pdu() to *not* consume a reference call skb_get() before.

Fixes: b85ab56c3f81 ("llc: properly handle dev_queue_xmit() return value")
Reported-by: syzbot+6b825a6494a04cc0e3f7@syzkaller.appspotmail.com
Signed-off-by: Eric Biggers <ebiggers@google.com>
Signed-off-by: Jakub Kicinski <jakub.kicinski@netronome.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
include/net/llc_conn.h | 2 +-
net/llc/llc_c_ac.c | 8 ++++++--
net/llc/llc_conn.c | 32 +++++++++-----------------------
3 files changed, 16 insertions(+), 26 deletions(-)

--- a/include/net/llc_conn.h
+++ b/include/net/llc_conn.h
@@ -104,7 +104,7 @@ void llc_sk_reset(struct sock *sk);

/* Access to a connection */
int llc_conn_state_process(struct sock *sk, struct sk_buff *skb);
-int llc_conn_send_pdu(struct sock *sk, struct sk_buff *skb);
+void llc_conn_send_pdu(struct sock *sk, struct sk_buff *skb);
void llc_conn_rtn_pdu(struct sock *sk, struct sk_buff *skb);
void llc_conn_resend_i_pdu_as_cmd(struct sock *sk, u8 nr, u8 first_p_bit);
void llc_conn_resend_i_pdu_as_rsp(struct sock *sk, u8 nr, u8 first_f_bit);
--- a/net/llc/llc_c_ac.c
+++ b/net/llc/llc_c_ac.c
@@ -372,6 +372,7 @@ int llc_conn_ac_send_i_cmd_p_set_1(struc
llc_pdu_init_as_i_cmd(skb, 1, llc->vS, llc->vR);
rc = llc_mac_hdr_init(skb, llc->dev->dev_addr, llc->daddr.mac);
if (likely(!rc)) {
+ skb_get(skb);
llc_conn_send_pdu(sk, skb);
llc_conn_ac_inc_vs_by_1(sk, skb);
}
@@ -389,7 +390,8 @@ static int llc_conn_ac_send_i_cmd_p_set_
llc_pdu_init_as_i_cmd(skb, 0, llc->vS, llc->vR);
rc = llc_mac_hdr_init(skb, llc->dev->dev_addr, llc->daddr.mac);
if (likely(!rc)) {
- rc = llc_conn_send_pdu(sk, skb);
+ skb_get(skb);
+ llc_conn_send_pdu(sk, skb);
llc_conn_ac_inc_vs_by_1(sk, skb);
}
return rc;
@@ -406,6 +408,7 @@ int llc_conn_ac_send_i_xxx_x_set_0(struc
llc_pdu_init_as_i_cmd(skb, 0, llc->vS, llc->vR);
rc = llc_mac_hdr_init(skb, llc->dev->dev_addr, llc->daddr.mac);
if (likely(!rc)) {
+ skb_get(skb);
llc_conn_send_pdu(sk, skb);
llc_conn_ac_inc_vs_by_1(sk, skb);
}
@@ -916,7 +919,8 @@ static int llc_conn_ac_send_i_rsp_f_set_
llc_pdu_init_as_i_cmd(skb, llc->ack_pf, llc->vS, llc->vR);
rc = llc_mac_hdr_init(skb, llc->dev->dev_addr, llc->daddr.mac);
if (likely(!rc)) {
- rc = llc_conn_send_pdu(sk, skb);
+ skb_get(skb);
+ llc_conn_send_pdu(sk, skb);
llc_conn_ac_inc_vs_by_1(sk, skb);
}
return rc;
--- a/net/llc/llc_conn.c
+++ b/net/llc/llc_conn.c
@@ -30,7 +30,7 @@
#endif

static int llc_find_offset(int state, int ev_type);
-static int llc_conn_send_pdus(struct sock *sk, struct sk_buff *skb);
+static void llc_conn_send_pdus(struct sock *sk);
static int llc_conn_service(struct sock *sk, struct sk_buff *skb);
static int llc_exec_conn_trans_actions(struct sock *sk,
struct llc_conn_state_trans *trans,
@@ -193,11 +193,11 @@ out_skb_put:
return rc;
}

-int llc_conn_send_pdu(struct sock *sk, struct sk_buff *skb)
+void llc_conn_send_pdu(struct sock *sk, struct sk_buff *skb)
{
/* queue PDU to send to MAC layer */
skb_queue_tail(&sk->sk_write_queue, skb);
- return llc_conn_send_pdus(sk, skb);
+ llc_conn_send_pdus(sk);
}

/**
@@ -255,7 +255,7 @@ void llc_conn_resend_i_pdu_as_cmd(struct
if (howmany_resend > 0)
llc->vS = (llc->vS + 1) % LLC_2_SEQ_NBR_MODULO;
/* any PDUs to re-send are queued up; start sending to MAC */
- llc_conn_send_pdus(sk, NULL);
+ llc_conn_send_pdus(sk);
out:;
}

@@ -296,7 +296,7 @@ void llc_conn_resend_i_pdu_as_rsp(struct
if (howmany_resend > 0)
llc->vS = (llc->vS + 1) % LLC_2_SEQ_NBR_MODULO;
/* any PDUs to re-send are queued up; start sending to MAC */
- llc_conn_send_pdus(sk, NULL);
+ llc_conn_send_pdus(sk);
out:;
}

@@ -340,16 +340,12 @@ out:
/**
* llc_conn_send_pdus - Sends queued PDUs
* @sk: active connection
- * @hold_skb: the skb held by caller, or NULL if does not care
*
- * Sends queued pdus to MAC layer for transmission. When @hold_skb is
- * NULL, always return 0. Otherwise, return 0 if @hold_skb is sent
- * successfully, or 1 for failure.
+ * Sends queued pdus to MAC layer for transmission.
*/
-static int llc_conn_send_pdus(struct sock *sk, struct sk_buff *hold_skb)
+static void llc_conn_send_pdus(struct sock *sk)
{
struct sk_buff *skb;
- int ret = 0;

while ((skb = skb_dequeue(&sk->sk_write_queue)) != NULL) {
struct llc_pdu_sn *pdu = llc_pdu_sn_hdr(skb);
@@ -361,20 +357,10 @@ static int llc_conn_send_pdus(struct soc
skb_queue_tail(&llc_sk(sk)->pdu_unack_q, skb);
if (!skb2)
break;
- dev_queue_xmit(skb2);
- } else {
- bool is_target = skb == hold_skb;
- int rc;
-
- if (is_target)
- skb_get(skb);
- rc = dev_queue_xmit(skb);
- if (is_target)
- ret = rc;
+ skb = skb2;
}
+ dev_queue_xmit(skb);
}
-
- return ret;
}

/**