From: Petr Machata petrm@nvidia.com
[ Upstream commit 0caf6d9922192dd1afa8dc2131abfb4df1443b9f ]
When a netlink message is received, netlink_recvmsg() fills in the address of the sender. One of the fields is the 32-bit bitfield nl_groups, which carries the multicast group on which the message was received. The least significant bit corresponds to group 1, and therefore the highest group that the field can represent is 32. Above that, the UB sanitizer flags the out-of-bounds shift attempts.
Which bits end up being set in such case is implementation defined, but it's either going to be a wrong non-zero value, or zero, which is at least not misleading. Make the latter choice deterministic by always setting to 0 for higher-numbered multicast groups.
To get information about membership in groups >= 32, userspace is expected to use nl_pktinfo control messages[0], which are enabled by NETLINK_PKTINFO socket option. [0] https://lwn.net/Articles/147608/
The way to trigger this issue is e.g. through monitoring the BRVLAN group:
# bridge monitor vlan & # ip link add name br type bridge
Which produces the following citation:
UBSAN: shift-out-of-bounds in net/netlink/af_netlink.c:162:19 shift exponent 32 is too large for 32-bit type 'int'
Fixes: f7fa9b10edbb ("[NETLINK]: Support dynamic number of multicast groups per netlink family") Signed-off-by: Petr Machata petrm@nvidia.com Reviewed-by: Ido Schimmel idosch@nvidia.com Link: https://lore.kernel.org/r/2bef6aabf201d1fc16cca139a744700cff9dcb04.164752763... Signed-off-by: Jakub Kicinski kuba@kernel.org Signed-off-by: Sasha Levin sashal@kernel.org --- net/netlink/af_netlink.c | 2 ++ 1 file changed, 2 insertions(+)
diff --git a/net/netlink/af_netlink.c b/net/netlink/af_netlink.c index 81ba8e51e01f..83ca93b32f5f 100644 --- a/net/netlink/af_netlink.c +++ b/net/netlink/af_netlink.c @@ -157,6 +157,8 @@ EXPORT_SYMBOL(do_trace_netlink_extack);
static inline u32 netlink_group_mask(u32 group) { + if (group > 32) + return 0; return group ? 1 << (group - 1) : 0; }