ipv4: Mask upper DSCP bits and ECN bits in NETLINK_FIB_LOOKUP family

[ Upstream commit 8fed54758cd248cd311a2b5c1e180abef1866237 ]

The NETLINK_FIB_LOOKUP netlink family can be used to perform a FIB
lookup according to user provided parameters and communicate the result
back to user space.

However, unlike other users of the FIB lookup API, the upper DSCP bits
and the ECN bits of the DS field are not masked, which can result in the
wrong result being returned.

Solve this by masking the upper DSCP bits and the ECN bits using
IPTOS_RT_MASK.

The structure that communicates the request and the response is not
exported to user space, so it is unlikely that this netlink family is
actually in use [1].

[1] https://lore.kernel.org/netdev/ZpqpB8vJU%2FQ6LSqa@debian/

Signed-off-by: Ido Schimmel <idosch@nvidia.com>
Reviewed-by: Guillaume Nault <gnault@redhat.com>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>

diff --git a/net/ipv4/fib_frontend.c b/net/ipv4/fib_frontend.c
index 41f890bf9d4c4559e2a093051cd08977b9ab97d4..0394146f813c5891e51e6d370e53709ae666d991 100644 (file)
--- a/net/ipv4/fib_frontend.c
+++ b/net/ipv4/fib_frontend.c
@@ -1334,7 +1334,7 @@ static void nl_fib_lookup(struct net *net, struct fib_result_nl *frn)
        struct flowi4           fl4 = {
                .flowi4_mark = frn->fl_mark,
                .daddr = frn->fl_addr,
-               .flowi4_tos = frn->fl_tos,
+               .flowi4_tos = frn->fl_tos & IPTOS_RT_MASK,
                .flowi4_scope = frn->fl_scope,
        };
        struct fib_table *tb;