wext: fix alignment problem in serializing 'struct iw_point'
This fixes a typo in the definition of the serialized length of struct iw_point:
a) wireless.h is exported to userspace, the typo causes IW_EV_POINT_PK_LEN
to be 12 on 64-bit, and 8 on 32-bit systems (causing misalignment);
b) in compat-64 mode iwe_stream_add_point() memcpys overlap (see below).
The second case in in compat-64 mode looks like (variable names are as in
include/net/iw_handler.h:iwe_stream_add_point()):
point_len = IW_EV_COMPAT_POINT_LEN = 8
lcp_len = IW_EV_COMPAT_LCP_LEN = 4
2nd memcpy: IW_EV_POINT_PK_LEN - IW_EV_LCP_PK_LEN = 12 - 4 = 8
IW_EV_LCP_PK_LEN
<--------------> *---> 'extra' data area
+-------+-------+-------+-------+---------------+------- ...-+
| len | cmd |length | flags | (empty) -> extra ... |
+-------+-------+-------+-------+---------------+------- ...-+
2 2 2 2 4
lcp_len
<--------------> <-!! OVERLAP !!>
<--1st memcpy--><------- 2nd memcpy ----------->
<---- 3rd memcpy ------- ... >
<--------- point_len ---------->
This case could cause overrun whenever iw_point.length < 4.
The other two cases are -
* 32-bit systems: IW_EV_POINT_PK_LEN - IW_EV_LCP_PK_LEN = 8 - 4 = 4,
the second memcpy copies exactly the 4 required bytes;
* 64-bit systems: IW_EV_POINT_PK_LEN - IW_EV_LCP_PK_LEN = 12 - 4 = 8,
the second memcpy copies a superfluous (but non overlapping) 4 bytes.
The patch changes IW_EV_POINT_PK_LEN to be 8, so that in all 3 cases always only
the requested iw_point.{length,flags} (both __u16) are copied, avoiding overrrun
(compat-64) and superfluous copy (64-bit). In addition, the userspace header is
sanitized (in agreement with version 30 of the wireless tools).
Many thanks to Johannes Berg for help and review with this patch.
Signed-off-by: Gerrit Renker <gerrit@erg.abdn.ac.uk>
Signed-off-by: John W. Linville <linville@tuxdriver.com>
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