Commit 85893120 authored Oct 27, 2010 by Jeff Mahoney Committed by Linus Torvalds Oct 27, 2010

delayacct: align to 8 byte boundary on 64-bit systems



prepare_reply() sets up an skb for the response.  The payload contains:

 +--------------------------------+
 | genlmsghdr - 4 bytes           |
 +--------------------------------+
 | NLA header - 4 bytes           | /* Aggregate header */
 +-+------------------------------+
 | | NLA header - 4 bytes         | /* PID header */
 | +------------------------------+
 | | pid/tgid   - 4 bytes         |
 | +------------------------------+
 | | NLA header - 4 bytes         | /* stats header */
 | + -----------------------------+ <- oops. aligned on 4 byte boundary
 | | struct taskstats - 328 bytes |
 +-+------------------------------+

The start of the taskstats struct must be 8 byte aligned on IA64 (and
other systems with 8 byte alignment rules for 64-bit types) or runtime
alignment warnings will be issued.

This patch pads the pid/tgid field out to sizeof(long), which forces the
alignment of taskstats.  The getdelays userspace code is ok with this
since it assumes 32-bit pid/tgid and then honors that header's length
field.

An array is used to avoid exposing kernel memory contents to userspace in
the response.

Signed-off-by: Jeff Mahoney <jeffm@suse.com>
Cc: Balbir Singh <balbir@in.ibm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

parent db9e5679

kernel/taskstats.c

+7 −1

Original line number	Diff line number	Diff line
		@@ -360,6 +360,12 @@ static struct taskstats mk_reply(struct sk_buff skb, int type, u32 pid)
		struct nlattr na, ret;
		int aggr;

		/* If we don't pad, we end up with alignment on a 4 byte boundary.
		* This causes lots of runtime warnings on systems requiring 8 byte
		* alignment */
		u32 pids[2] = { pid, 0 };
		int pid_size = ALIGN(sizeof(pid), sizeof(long));

		aggr = (type == TASKSTATS_TYPE_PID)
		? TASKSTATS_TYPE_AGGR_PID
		: TASKSTATS_TYPE_AGGR_TGID;
		@@ -367,7 +373,7 @@ static struct taskstats mk_reply(struct sk_buff skb, int type, u32 pid)
		na = nla_nest_start(skb, aggr);
		if (!na)
		goto err;
		if (nla_put(skb, type, sizeof(pid), &pid) < 0)
		if (nla_put(skb, type, pid_size, pids) < 0)
		goto err;
		ret = nla_reserve(skb, TASKSTATS_TYPE_STATS, sizeof(struct taskstats));
		if (!ret)

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