commit 19be0ea upstream.

faultin_page drops FOLL_WRITE after the page fault handler did the CoW
and then we retry follow_page_mask to get our CoWed page. This is racy,
however because the page might have been unmapped by that time and so
we would have to do a page fault again, this time without CoW. This
would cause the page cache corruption for FOLL_FORCE on MAP_PRIVATE
read only mappings with obvious consequences.

This is an ancient bug that was actually already fixed once by Linus
eleven years ago in commit 4ceb5db ("Fix get_user_pages() race
for write access") but that was then undone due to problems on s390
by commit f33ea7f ("fix get_user_pages bug") because s390 didn't
have proper dirty pte tracking until abf09be ("s390/mm: implement
software dirty bits"). This wasn't a problem at the time as pointed out
by Hugh Dickins because madvise relied on mmap_sem for write up until
0a27a14 ("mm: madvise avoid exclusive mmap_sem") but since then we
can race with madvise which can unmap the fresh COWed page or with KSM
and corrupt the content of the shared page.

This patch is based on the Linus' approach to not clear FOLL_WRITE after
the CoW page fault (aka VM_FAULT_WRITE) but instead introduces FOLL_COW
to note this fact. The flag is then rechecked during follow_pfn_pte to
enforce the page fault again if we do not see the CoWed page. Linus was
suggesting to check pte_dirty again as s390 is OK now. But that would
make backporting to some old kernels harder. So instead let's just make
sure that vm_normal_page sees a pure anonymous page.

This would guarantee we are seeing a real CoW page. Introduce
can_follow_write_pte which checks both pte_write and falls back to
PageAnon on forced write faults which passed CoW already. Thanks to Hugh
to point out that a special care has to be taken for KSM pages because
our COWed page might have been merged with a KSM one and keep its
PageAnon flag.

Fixes: 0a27a14 ("mm: madvise avoid exclusive mmap_sem")
Reported-by: Phil "not Paul" Oester <[email protected]>
Disclosed-by: Andy Lutomirski <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>
Signed-off-by: Michal Hocko <[email protected]>
[bwh: Backported to 3.2:
 - Adjust filename, context, indentation
 - The 'no_page' exit path in follow_page() is different, so open-code the
   cleanup
 - Delete a now-unused label]
Signed-off-by: Ben Hutchings <[email protected]>
Signed-off-by: Nico Isenbeck <[email protected]>

update fbtft to latest git version

This reverts commit e535609.

In the current DCCP implementation an skb for a DCCP_PKT_REQUEST packet
is forcibly freed via __kfree_skb in dccp_rcv_state_process if
dccp_v6_conn_request successfully returns.

However, if IPV6_RECVPKTINFO is set on a socket, the address of the skb
is saved to ireq->pktopts and the ref count for skb is incremented in
dccp_v6_conn_request, so skb is still in use. Nevertheless, it gets freed
in dccp_rcv_state_process.

Fix by calling consume_skb instead of doing goto discard and therefore
calling __kfree_skb.

Similar fixes for TCP:

fb7e239 [TCP]: skb is unexpectedly freed.
0aea76d tcp: SYN packets are now
simply consumed

Signed-off-by: Andrey Konovalov <[email protected]>
Acked-by: Eric Dumazet <[email protected]>
Signed-off-by: David S. Miller <[email protected]>
Signed-off-by: Nico Isenbeck <[email protected]>