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authorPavel Skripkin <paskripkin@gmail.com>2021-07-25 00:11:59 +0300
committerDavid S. Miller <davem@davemloft.net>2021-07-27 15:05:56 +0300
commitc7c9d2102c9c098916ab9e0ab248006107d00d6c (patch)
tree5ddc2a37ffd3d60faf85893f4ab06045e44d5327 /net
parentfcef709c2c4baf758950bd7395e4b10527b81e2c (diff)
downloadlinux-c7c9d2102c9c098916ab9e0ab248006107d00d6c.tar.xz
net: llc: fix skb_over_panic
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>
Diffstat (limited to 'net')
-rw-r--r--net/llc/af_llc.c10
-rw-r--r--net/llc/llc_s_ac.c2
2 files changed, 10 insertions, 2 deletions
diff --git a/net/llc/af_llc.c b/net/llc/af_llc.c
index 7180979114e4..ac5cadd02cfa 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 b554f26c68ee..79d1cef8f15a 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);