[PATCH] net: genetlink: Fix memleak in genl_family_rcv_msg_dumpit()

[PATCH] net: genetlink: Fix memleak in genl_family_rcv_msg_dumpit()

[YueHaibing]

dumpit info is freed by cb->done now (genl_lock_done()/
genl_parallel_done()), however if any error occurs before
cb->done is called, info and attrs will leak.

unreferenced object 0xffff888119904840 (size 32):
comm "syz-executor.0", pid 857, jiffies 4295306979 (age 18.692s)
hex dump (first 32 bytes):
60 2d 5a af ff ff ff ff c0 d6 a5 ae ff ff ff ff `-Z.............
00 00 00 00 00 00 00 00 60 b4 25 ac ff ff ff ff ........`.%.....
backtrace:
[<0000000048573ee1>] kmalloc include/linux/slab.h:555 [inline]
[<0000000048573ee1>] genl_dumpit_info_alloc net/netlink/genetlink.c:463 [inline]
[<0000000048573ee1>] genl_family_rcv_msg_dumpit net/netlink/genetlink.c:598 [inline]
[<0000000048573ee1>] genl_family_rcv_msg net/netlink/genetlink.c:715 [inline]
[<0000000048573ee1>] genl_rcv_msg+0x7b7/0xce0 net/netlink/genetlink.c:735
[<000000006d27610a>] netlink_rcv_skb+0x139/0x390 net/netlink/af_netlink.c:2469
[<00000000d643c808>] genl_rcv+0x24/0x40 net/netlink/genetlink.c:746
[<00000000fdec3fc5>] netlink_unicast_kernel net/netlink/af_netlink.c:1303 [inline]
[<00000000fdec3fc5>] netlink_unicast+0x4a0/0x6a0 net/netlink/af_netlink.c:1329
[<0000000027eb500d>] netlink_sendmsg+0x793/0xc80 net/netlink/af_netlink.c:1918
[<000000006e6952a8>] sock_sendmsg_nosec net/socket.c:652 [inline]
[<000000006e6952a8>] sock_sendmsg+0x139/0x170 net/socket.c:672

Fixes: 1927f41a22a0 ("net: genetlink: introduce dump info struct to be available during dumpit op")
Signed-off-by: YueHaibing <yuehaibing@huawei.com>
---
 net/netlink/genetlink.c | 8 +++-----
 1 file changed, 3 insertions(+), 5 deletions(-)

diff --git a/net/netlink/genetlink.c b/net/netlink/genetlink.c
index 9f357aa22b94..cd719aecb0e2 100644
--- a/net/netlink/genetlink.c
+++ b/net/netlink/genetlink.c
@@ -548,8 +548,6 @@ static int genl_lock_done(struct netlink_callback *cb)
 		rc = ops->done(cb);
 		genl_unlock();
 	}
-	genl_family_rcv_msg_attrs_free(info->family, info->attrs, true);
-	genl_dumpit_info_free(info);
 	return rc;
 }
 
@@ -561,8 +559,6 @@ static int genl_parallel_done(struct netlink_callback *cb)
 
 	if (ops->done)
 		rc = ops->done(cb);
-	genl_family_rcv_msg_attrs_free(info->family, info->attrs, true);
-	genl_dumpit_info_free(info);
 	return rc;
 }
 
@@ -594,7 +590,6 @@ static int genl_family_rcv_msg_dumpit(const struct genl_family *family,
 		return PTR_ERR(attrs);
 
 no_attrs:
-	/* Allocate dumpit info. It is going to be freed by done() callback. */
 	info = genl_dumpit_info_alloc();
 	if (!info) {
 		genl_family_rcv_msg_attrs_free(family, attrs, true);
@@ -630,6 +625,9 @@ static int genl_family_rcv_msg_dumpit(const struct genl_family *family,
 		err = __netlink_dump_start(net->genl_sock, skb, nlh, &c);
 	}
 
+	genl_family_rcv_msg_attrs_free(info->family, info->attrs, true);
+	genl_dumpit_info_free(info);
+
 	return err;
 }
 
-- 
2.20.1

Re: [PATCH] net: genetlink: Fix memleak in genl_family_rcv_msg_dumpit()

[Cong Wang]

On Mon, Jun 1, 2020 at 11:47 PM YueHaibing <yuehaibing@huawei.com> wrote:
> @@ -630,6 +625,9 @@ static int genl_family_rcv_msg_dumpit(const struct genl_family *family,
>                 err = __netlink_dump_start(net->genl_sock, skb, nlh, &c);
>         }
>
> +       genl_family_rcv_msg_attrs_free(info->family, info->attrs, true);
> +       genl_dumpit_info_free(info);
> +
>         return err;
>  }

I do not think you can just move it after __netlink_dump_start(),
because cb->done() can be called, for example, in netlink_sock_destruct()
too.

Re: [PATCH] net: genetlink: Fix memleak in genl_family_rcv_msg_dumpit()

[Yuehaibing]

On 2020/6/3 2:04, Cong Wang wrote:
> On Mon, Jun 1, 2020 at 11:47 PM YueHaibing <yuehaibing@huawei.com> wrote:
>> @@ -630,6 +625,9 @@ static int genl_family_rcv_msg_dumpit(const struct genl_family *family,
>>                 err = __netlink_dump_start(net->genl_sock, skb, nlh, &c);
>>         }
>>
>> +       genl_family_rcv_msg_attrs_free(info->family, info->attrs, true);
>> +       genl_dumpit_info_free(info);
>> +
>>         return err;
>>  }
> 
> I do not think you can just move it after __netlink_dump_start(),
> because cb->done() can be called, for example, in netlink_sock_destruct()
> too.

netlink_sock_destruct() call cb->done() while nlk->cb_running is true,

if nlk->cb_running is not set to true in __netlink_dump_start() before return,

the memleak still occurs.

> 
>