From: Pavel Skripkin paskripkin@gmail.com
[ 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: 1da177e4c3f4 ("Linux-2.6.12-rc2") Reported-and-tested-by: syzbot+5e5a981ad7cc54c4b2b4@syzkaller.appspotmail.com Signed-off-by: Pavel Skripkin paskripkin@gmail.com Signed-off-by: David S. Miller davem@davemloft.net Signed-off-by: Sasha Levin sashal@kernel.org --- include/net/llc_pdu.h | 31 +++++++++++++++++++++++-------- net/llc/af_llc.c | 10 +++++++++- net/llc/llc_s_ac.c | 2 +- 3 files changed, 33 insertions(+), 10 deletions(-)
diff --git a/include/net/llc_pdu.h b/include/net/llc_pdu.h index c0f0a13ed818..49aa79c7b278 100644 --- a/include/net/llc_pdu.h +++ b/include/net/llc_pdu.h @@ -15,9 +15,11 @@ #include <linux/if_ether.h>
/* Lengths of frame formats */ -#define LLC_PDU_LEN_I 4 /* header and 2 control bytes */ -#define LLC_PDU_LEN_S 4 -#define LLC_PDU_LEN_U 3 /* header and 1 control byte */ +#define LLC_PDU_LEN_I 4 /* header and 2 control bytes */ +#define LLC_PDU_LEN_S 4 +#define LLC_PDU_LEN_U 3 /* header and 1 control byte */ +/* header and 1 control byte and XID info */ +#define LLC_PDU_LEN_U_XID (LLC_PDU_LEN_U + sizeof(struct llc_xid_info)) /* Known SAP addresses */ #define LLC_GLOBAL_SAP 0xFF #define LLC_NULL_SAP 0x00 /* not network-layer visible */ @@ -50,9 +52,10 @@ #define LLC_PDU_TYPE_U_MASK 0x03 /* 8-bit control field */ #define LLC_PDU_TYPE_MASK 0x03
-#define LLC_PDU_TYPE_I 0 /* first bit */ -#define LLC_PDU_TYPE_S 1 /* first two bits */ -#define LLC_PDU_TYPE_U 3 /* first two bits */ +#define LLC_PDU_TYPE_I 0 /* first bit */ +#define LLC_PDU_TYPE_S 1 /* first two bits */ +#define LLC_PDU_TYPE_U 3 /* first two bits */ +#define LLC_PDU_TYPE_U_XID 4 /* private type for detecting XID commands */
#define LLC_PDU_TYPE_IS_I(pdu) \ ((!(pdu->ctrl_1 & LLC_PDU_TYPE_I_MASK)) ? 1 : 0) @@ -230,9 +233,18 @@ static inline struct llc_pdu_un *llc_pdu_un_hdr(struct sk_buff *skb) static inline void llc_pdu_header_init(struct sk_buff *skb, u8 type, u8 ssap, u8 dsap, u8 cr) { - const int hlen = type == LLC_PDU_TYPE_U ? 3 : 4; + int hlen = 4; /* default value for I and S types */ struct llc_pdu_un *pdu;
+ switch (type) { + case LLC_PDU_TYPE_U: + hlen = 3; + break; + case LLC_PDU_TYPE_U_XID: + hlen = 6; + break; + } + skb_push(skb, hlen); skb_reset_network_header(skb); pdu = llc_pdu_un_hdr(skb); @@ -374,7 +386,10 @@ static inline void llc_pdu_init_as_xid_cmd(struct sk_buff *skb, xid_info->fmt_id = LLC_XID_FMT_ID; /* 0x81 */ xid_info->type = svcs_supported; xid_info->rw = rx_window << 1; /* size of receive window */ - skb_put(skb, sizeof(struct llc_xid_info)); + + /* no need to push/put since llc_pdu_header_init() has already + * pushed 3 + 3 bytes + */ }
/** diff --git a/net/llc/af_llc.c b/net/llc/af_llc.c index fa0f3c1543ba..0b3adf7594ff 100644 --- a/net/llc/af_llc.c +++ b/net/llc/af_llc.c @@ -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; diff --git a/net/llc/llc_s_ac.c b/net/llc/llc_s_ac.c index 7ae4cc684d3a..9fa3342c7a82 100644 --- a/net/llc/llc_s_ac.c +++ b/net/llc/llc_s_ac.c @@ -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);