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net: llc: fix skb_over_panic

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[ Upstream commit c7c9d2102c9c098916ab9e0ab248006107d00d6c ]

Syzbot reported skb_over_panic() in llc_pdu_init_as_xid_cmd(). The
problem was in wrong LCC header manipulations.

Syzbot's reproducer tries to send XID packet. llc_ui_sendmsg() is
doing following steps:

	1. skb allocation with size = len + header size
		len is passed from userpace and header size
		is 3 since addr->sllc_xid is set.

	2. skb_reserve() for header_len = 3
	3. filling all other space with memcpy_from_msg()

Ok, at this moment we have fully loaded skb, only headers needs to be
filled.

Then code comes to llc_sap_action_send_xid_c(). This function pushes 3
bytes for LLC PDU header and initializes it. Then comes
llc_pdu_init_as_xid_cmd(). It initalizes next 3 bytes *AFTER* LLC PDU
header and call skb_push(skb, 3). This looks wrong for 2 reasons:

	1. Bytes rigth after LLC header are user data, so this function
	   was overwriting payload.

	2. skb_push(skb, 3) call can cause skb_over_panic() since
	   all free space was filled in llc_ui_sendmsg(). (This can
	   happen is user passed 686 len: 686 + 14 (eth header) + 3 (LLC
	   header) = 703. SKB_DATA_ALIGN(703) = 704)

So, in this patch I added 2 new private constansts: LLC_PDU_TYPE_U_XID
and LLC_PDU_LEN_U_XID. LLC_PDU_LEN_U_XID is used to correctly reserve
header size to handle LLC + XID case. LLC_PDU_TYPE_U_XID is used by
llc_pdu_header_init() function to push 6 bytes instead of 3. And finally
I removed skb_push() call from llc_pdu_init_as_xid_cmd().

This changes should not affect other parts of LLC, since after
all steps we just transmit buffer.

Fixes: 1da177e4c3 ("Linux-2.6.12-rc2")
Reported-and-tested-by: [email protected]
Signed-off-by: Pavel Skripkin <[email protected]>
Signed-off-by: David S. Miller <[email protected]>
Signed-off-by: Sasha Levin <[email protected]>
This commit is contained in:
Pavel Skripkin 2021-07-25 00:11:59 +03:00 • committed by Greg Kroah-Hartman
commit 527feae56f
3 changed files with 33 additions and 10 deletions
Download patch file Download diff file Expand all files Collapse all files

10
net/llc/af_llc.c
View file

@ -98,8 +98,16 @@ static inline u8 llc_ui_header_len(struct sock *sk, struct sockaddr_llc *addr)
{
u8 rc = LLC_PDU_LEN_U;
if (addr->sllc_test || addr->sllc_xid)
if (addr->sllc_test)
rc = LLC_PDU_LEN_U;
else if (addr->sllc_xid)
/* We need to expand header to sizeof(struct llc_xid_info)
* since llc_pdu_init_as_xid_cmd() sets 4,5,6 bytes of LLC header
* as XID PDU. In llc_ui_sendmsg() we reserved header size and then
* filled all other space with user data. If we won't reserve this
* bytes, llc_pdu_init_as_xid_cmd() will overwrite user data
*/
rc = LLC_PDU_LEN_U_XID;
else if (sk->sk_type == SOCK_STREAM)
rc = LLC_PDU_LEN_I;
return rc;

2
net/llc/llc_s_ac.c
View file

@ -79,7 +79,7 @@ int llc_sap_action_send_xid_c(struct llc_sap *sap, struct sk_buff *skb)
struct llc_sap_state_ev *ev = llc_sap_ev(skb);
int rc;
llc_pdu_header_init(skb, LLC_PDU_TYPE_U, ev->saddr.lsap,
llc_pdu_header_init(skb, LLC_PDU_TYPE_U_XID, ev->saddr.lsap,
ev->daddr.lsap, LLC_PDU_CMD);
llc_pdu_init_as_xid_cmd(skb, LLC_XID_NULL_CLASS_2, 0);
rc = llc_mac_hdr_init(skb, ev->saddr.mac, ev->daddr.mac);