]> git.baikalelectronics.ru Git - kernel.git/commit
net: codel: Avoid undefined behavior from signed overflow
authorJesper Dangaard Brouer <netoptimizer@brouer.com>
Thu, 31 Oct 2013 21:10:55 +0000 (22:10 +0100)
committerDavid S. Miller <davem@davemloft.net>
Tue, 5 Nov 2013 01:01:29 +0000 (20:01 -0500)
commit255ce829ed0b0584e61f112cc783d2b75faa8bdb
tree3308ce1f1b158b507f802561cda5fde8866bf8e7
parent1dd294004c3181b4b5bcb6fe9167750f883adbcf
net: codel: Avoid undefined behavior from signed overflow

As described in commit 8dc006544 (jiffies: Avoid undefined
behavior from signed overflow), according to the C standard
3.4.3p3, overflow of a signed integer results in undefined
behavior.

To fix this, do as the above commit, and do an unsigned
subtraction, and interpreting the result as a signed
two's-complement number.  This is based on the theory from
RFC 1982 and is nicely described in wikipedia here:
 https://en.wikipedia.org/wiki/Serial_number_arithmetic#General_Solution

A side-note, I have seen practical issues with the previous logic
when dealing with 16-bit, on a 64-bit machine (gcc version
4.4.5). This were 32-bit, which I have not observed issues with.

Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Signed-off-by: Jesper Dangaard Brouer <netoptimizer@brouer.com>
Acked-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
include/net/codel.h