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c7c9d2102c
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:
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|---|---|---|
| .. | ||
| acpi | ||
| asm-generic | ||
| clocksource | ||
| crypto | ||
| drm | ||
| dt-bindings | ||
| keys | ||
| kunit | ||
| kvm | ||
| linux | ||
| math-emu | ||
| media | ||
| memory | ||
| misc | ||
| net | ||
| pcmcia | ||
| ras | ||
| rdma | ||
| scsi | ||
| soc | ||
| sound | ||
| target | ||
| trace | ||
| uapi | ||
| vdso | ||
| video | ||
| xen | ||