Description: net/ipv4: divide by 0 in __tcp_select_window()
References:
 https://groups.google.com/forum/#!topic/syzkaller/e4SrsEBEziQ
Notes:
 bwh> This might not be possible in earlier versions, but it does look
 bwh> plausible and the fix should have no effect if it's not possible.
Bugs:
upstream: released (4.12-rc3) [499350a5a6e7512d9ed369ed63a4244b6536f4f8]
4.9-upstream-stable: released (4.9.51) [a10c510179b369f7d1e8cf77f43ee2db900c1ac9]
3.16-upstream-stable: released (3.16.48) [32cb2d4a59d0512aa825e7f0352f66063482cc07]
3.2-upstream-stable: released (3.2.93) [16a0303d3f6b222044de5d33c01cbdf590050473]
sid: released (4.12.6-1)
4.9-stretch-security: released (4.9.30-2+deb9u4) [bugfix/all/tcp-initialize-rcv_mss-to-tcp_min_mss-instead-of-0.patch]
3.16-jessie-security: released (3.16.43-2+deb8u4) [bugfix/all/tcp-initialize-rcv_mss-to-tcp_min_mss-instead-of-0.patch]
3.2-wheezy-security: released (3.2.93-1)