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| author | Pavel Skripkin <paskripkin@gmail.com> | 2021-07-25 00:11:59 +0300 |
|---|---|---|
| committer | David S. Miller <davem@davemloft.net> | 2021-07-27 13:05:56 +0100 |
| commit | c7c9d2102c9c098916ab9e0ab248006107d00d6c (patch) | |
| tree | 5ddc2a37ffd3d60faf85893f4ab06045e44d5327 /net/llc | |
| parent | fcef709c2c4baf758950bd7395e4b10527b81e2c (diff) | |
| download | linux-c7c9d2102c9c098916ab9e0ab248006107d00d6c.tar.bz2 | |
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/llc')
| -rw-r--r-- | net/llc/af_llc.c | 10 | ||||
| -rw-r--r-- | net/llc/llc_s_ac.c | 2 |
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); |