On 04.09.2011 18:18, Michał Mirosław wrote: > On Sat, Sep 03, 2011 at 07:26:08PM +0200, kaber@xxxxxxxxx wrote: >> From: Patrick McHardy <kaber@xxxxxxxxx> >> >> Add support for memory mapped sendmsg() to netlink. Userspace queued to >> be processed frames into the TX ring and invokes sendmsg with >> msg.iov.iov_base = NULL to trigger processing of all pending messages. >> >> Since the kernel usually performs full message validation before beginning >> processing, userspace must be prevented from modifying the message >> contents while the kernel is processing them. In order to do so, the >> frames contents are copied to an allocated skb in case the the ring is >> mapped more than once or the file descriptor is shared (f.i. through >> AF_UNIX file descriptor passing). >> >> Otherwise an skb without a data area is allocated, the data pointer set >> to point to the data area of the ring frame and the skb is processed. >> Once the skb is freed, the destructor releases the frame back to userspace >> by setting the status to NL_MMAP_STATUS_UNUSED. > > Is this protected from threads? Like: one thread waits on sendmsg() and > another (same process) changes the buffer. Yes, if the ring is mapped multiple times (or the file descriptor is changed), the contents are copied to an allocated skb. -- To unsubscribe from this list: send the line "unsubscribe netfilter-devel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
