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>

diff --git a/kernel/taskstats.c b/kernel/taskstats.c
index 11281d5792bd5b4d0eb7d5b86034ca4b2a4d256a..5a651aa63d614c3c629f6ad8be24c451449d4bce 100644 (file)
--- a/kernel/taskstats.c
+++ b/kernel/taskstats.c
@@ -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)