relay: fix for possible loss/corruption of produced subbufs

Fix possible loss/corruption of produced subbufs in
relay_subbufs_consumed().

When buf->subbufs_produced wraps around after UINT_MAX and
buf->subbufs_consumed is still < UINT_MAX, the condition

	if (buf->subbufs_consumed > buf->subbufs_produced)

will be true even for certain valid values of subbufs_consumed.  This may
lead to loss or corruption of produced subbufs.

Signed-off-by: Aravind Srinivasan <raa.aars@gmail.com>
Cc: Tom Zanussi <tzanussi@gmail.com>
Cc: Tom Zanussi <zanussi@us.ibm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/kernel/relay.c b/kernel/relay.c
index 8f2179c..e92db8c 100644 (file)
--- a/kernel/relay.c
+++ b/kernel/relay.c
@@ -797,13 +797,15 @@ void relay_subbufs_consumed(struct rchan *chan,
        if (!chan)
                return;
 
-       if (cpu >= NR_CPUS || !chan->buf[cpu])
+       if (cpu >= NR_CPUS || !chan->buf[cpu] ||
+                                       subbufs_consumed > chan->n_subbufs)
                return;
 
        buf = chan->buf[cpu];
-       buf->subbufs_consumed += subbufs_consumed;
-       if (buf->subbufs_consumed > buf->subbufs_produced)
+       if (subbufs_consumed > buf->subbufs_produced - buf->subbufs_consumed)
                buf->subbufs_consumed = buf->subbufs_produced;
+       else
+               buf->subbufs_consumed += subbufs_consumed;
 }
 EXPORT_SYMBOL_GPL(relay_subbufs_consumed);