relay: fix subbuf_splice_actor() adding too many pages

If subbuf_pages was larger than the max number of pages the pipe
buffer will hold, subbuf_splice_actor() would happily go beyond
the array size.

Signed-off-by: Jens Axboe <jens.axboe@oracle.com>

1 files changed, 3 insertions, 2 deletions

diff --git a/kernel/relay.c b/kernel/relay.c
index d080b9d161a..4c035a8a248 100644
--- a/kernel/relay.c
+++ b/kernel/relay.c
@@ -1066,7 +1066,7 @@ static int subbuf_splice_actor(struct file *in,
                                unsigned int flags,
                                int *nonpad_ret)
 {
-        unsigned int pidx, poff, total_len, subbuf_pages, ret;
+        unsigned int pidx, poff, total_len, subbuf_pages, nr_pages, ret;
         struct rchan_buf *rbuf = in->private_data;
         unsigned int subbuf_size = rbuf->chan->subbuf_size;
         uint64_t pos = (uint64_t) *ppos;
@@ -1097,8 +1097,9 @@ static int subbuf_splice_actor(struct file *in,
         subbuf_pages = rbuf->chan->alloc_size >> PAGE_SHIFT;
         pidx = (read_start / PAGE_SIZE) % subbuf_pages;
         poff = read_start & ~PAGE_MASK;
+        nr_pages = min_t(unsigned int, subbuf_pages, PIPE_BUFFERS);
 
-        for (total_len = 0; spd.nr_pages < subbuf_pages; spd.nr_pages++) {
+        for (total_len = 0; spd.nr_pages < nr_pages; spd.nr_pages++) {
                 unsigned int this_len, this_end, private;
                 unsigned int cur_pos = read_start + total_len;