[PATCH 3.10 65/85] net: unix socket code abuses csum_partial

From: Greg Kroah-Hartman
Date: Thu Mar 20 2014 - 20:24:02 EST

3.10-stable review patch. If anyone has any objections, please let me know.


From: Anton Blanchard <anton@xxxxxxxxx>

commit 0a13404dd3bf4ea870e3d96270b5a382edca85c0 upstream.

The unix socket code is using the result of csum_partial to
hash into a lookup table:

unix_hash_fold(csum_partial(sunaddr, len, 0));

csum_partial is only guaranteed to produce something that can be
folded into a checksum, as its prototype explains:

* returns a 32-bit number suitable for feeding into itself
* or csum_tcpudp_magic

The 32bit value should not be used directly.

Depending on the alignment, the ppc64 csum_partial will return
different 32bit partial checksums that will fold into the same
16bit checksum.

This difference causes the following testcase (courtesy of
Gustavo) to sometimes fail:

#include <sys/socket.h>
#include <stdio.h>

int main()

int i = 1;
setsockopt(fd, SOL_SOCKET, SO_REUSEADDR, &i, 4);

struct sockaddr addr;
addr.sa_family = AF_LOCAL;
bind(fd, &addr, 2);

listen(fd, 128);

struct sockaddr_storage ss;
socklen_t sslen = (socklen_t)sizeof(ss);
getsockname(fd, (struct sockaddr*)&ss, &sslen);


if (connect(fd, (struct sockaddr*)&ss, sslen) == -1){
return 1;
return 0;

As suggested by davem, fix this by using csum_fold to fold the
partial 32bit checksum into a 16bit checksum before using it.

Signed-off-by: Anton Blanchard <anton@xxxxxxxxx>
Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

net/unix/af_unix.c | 3 +--
1 file changed, 1 insertion(+), 2 deletions(-)

--- a/net/unix/af_unix.c
+++ b/net/unix/af_unix.c
@@ -160,9 +160,8 @@ static inline void unix_set_secdata(stru

static inline unsigned int unix_hash_fold(__wsum n)
- unsigned int hash = (__force unsigned int)n;
+ unsigned int hash = (__force unsigned int)csum_fold(n);

- hash ^= hash>>16;
hash ^= hash>>8;
return hash&(UNIX_HASH_SIZE-1);

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