[patch v2] infiniband: uverbs: limit the number of entries

[Dan Carpenter <error27@gmail.com>]

If we don't limit cmd.ne then the multiplications can overflow.  This
will allocate a small amount of RAM successfully for the "resp" and
"wc" buffers.  The heap will get corrupted when we call ib_poll_cq().

Documentation/infiniband/user_verbs.txt suggests this function is meant
for unprivileged access.

I chose to limit the number of entries to 500.  That limits the
allocations to 26 kb of RAM at the most.

Also we don't necessarily fill the "resp" buffer so I changed the
kmalloc() to a kzalloc() to avoid an information leak.  And I changed
the wc allocation to kcalloc() as a cleanup.

CC: stable@kernel.org
Signed-off-by: Dan Carpenter <error27@gmail.com>

diff --git a/drivers/infiniband/core/uverbs.h b/drivers/infiniband/core/uverbs.h
--- a/drivers/infiniband/core/uverbs.h
+++ b/drivers/infiniband/core/uverbs.h
@@ -162,6 +162,7 @@ void ib_uverbs_srq_event_handler(struct ib_event *event, void *context_ptr);
 void ib_uverbs_event_handler(struct ib_event_handler *handler,
 			     struct ib_event *event);
 
+#define UVERBS_MAX_NUM_ENTRIES 500
 #define IB_UVERBS_DECLARE_CMD(name)					\
 	ssize_t ib_uverbs_##name(struct ib_uverbs_file *file,		\
 				 const char __user *buf, int in_len,	\
diff --git a/drivers/infiniband/core/uverbs_cmd.c b/drivers/infiniband/core/uverbs_cmd.c
--- a/drivers/infiniband/core/uverbs_cmd.c
+++ b/drivers/infiniband/core/uverbs_cmd.c
@@ -906,12 +906,15 @@ ssize_t ib_uverbs_poll_cq(struct ib_uverbs_file *file,
 	if (copy_from_user(&cmd, buf, sizeof cmd))
 		return -EFAULT;
 
+	if (cmd.ne > UVERBS_MAX_NUM_ENTRIES)
+		cmd.ne = UVERBS_MAX_NUM_ENTRIES;
+
-	wc = kmalloc(cmd.ne * sizeof *wc, GFP_KERNEL);
+	wc = kcalloc(cmd.ne, sizeof *wc, GFP_KERNEL);
 	if (!wc)
 		return -ENOMEM;
 
 	rsize = sizeof *resp + cmd.ne * sizeof(struct ib_uverbs_wc);
-	resp = kmalloc(rsize, GFP_KERNEL);
+	resp = kzalloc(rsize, GFP_KERNEL);
 	if (!resp) {
 		ret = -ENOMEM;
 		goto out_wc;