[PATCH net-next 1/3] net: warn about attempts to register negative ifindex

[Jakub Kicinski <kuba@kernel.org>]

Since the xarray changes we mix returning valid ifindex and negative
errno in a single int returned from dev_index_reserve(). This depends
on the fact that ifindexes can't be negative. Otherwise we may insert
into the xarray and return a very large negative value. This in turn
may break ERR_PTR().

OvS is susceptible to this problem and lacking validation (fix posted
separately for net).

Reject negative ifindex explicitly. Add a warning because the input
validation is better handled by the caller.

Signed-off-by: Jakub Kicinski <kuba@kernel.org>
---
Turns out concerns from reviewers that callers may not check bounds on
ifindex were legit...
---
 net/core/dev.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/net/core/dev.c b/net/core/dev.c
index 636b41f0b32d..17e6281e408c 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -9589,6 +9589,11 @@ static int dev_index_reserve(struct net *net, u32 ifindex)
 {
 	int err;
 
+	if (ifindex > INT_MAX) {
+		DEBUG_NET_WARN_ON_ONCE(1);
+		return -EINVAL;
+	}
+
 	if (!ifindex)
 		err = xa_alloc_cyclic(&net->dev_by_index, &ifindex, NULL,
 				      xa_limit_31b, &net->ifindex, GFP_KERNEL);
-- 
2.41.0