CVE-2026-74577net: mpls: initialize rtm_tos in mpls_getroute()

Official description

In the Linux kernel, the following vulnerability has been resolved: net: mpls: initialize rtm_tos in mpls_getroute() mpls_getroute() builds the RTM_NEWROUTE reply to an RTM_GETROUTE request by filling a struct rtmsg allocated from an skb whose data area is not zeroed (alloc_skb(NLMSG_GOODSIZE, ...)). It sets every field of the header except rtm_tos: r = nlmsg_data(nlh); r->rtm_family = AF_MPLS; r->rtm_dst_len = 20; r->rtm_src_len = 0; r->rtm_table = RT_TABLE_MAIN; r->rtm_type = RTN_UNICAST; r->rtm_scope = RT_SCOPE_UNIVERSE; r->rtm_protocol = rt->rt_protocol; r->rtm_flags = 0; struct rtmsg has no padding, so the one uninitialised byte rtm_tos (offset 3) is copied straight to user space on recvmsg(), leaking a byte of uninitialised heap memory. This is in contrast to mpls_dump_route(), which fills the very same header and does set rtm_tos = 0. Initialize rtm_tos to 0, matching mpls_dump_route(). Reproduced with KMSAN by adding an MPLS route and issuing a non-RTM_F_FIB_MATCH RTM_GETROUTE for its label: BUG: KMSAN: kernel-infoleak in _copy_to_iter+0x36c/0x33f0 _copy_to_iter+0x36c/0x33f0 __skb_datagram_iter+0x196/0x12c0 skb_copy_datagram_iter+0x5b/0x210 netlink_recvmsg+0x37b/0xef0 ... Uninit was created at: __alloc_skb+0x8ca/0x10e0 mpls_getroute+0x1280/0x3a40 rtnetlink_rcv_msg+0x1138/0x15a0 ... Byte 19 of 64 is uninitialized (byte 19 = nlmsghdr(16) + rtmsg offset 3 = rtm_tos)

Affected packages & fixed versions

Affected products (as reported)

References

• https://git.kernel.org/stable/c/248718fd88b146d8bdc7610ecd1eb4cd16e0b5a1
• https://git.kernel.org/stable/c/466b474a8deb0c93b5280c6d261e5eda6482eca7
• https://git.kernel.org/stable/c/ba56f88aab18d982f2a21f11390f4d8a8897782a
• https://git.kernel.org/stable/c/95651461cf77cc6590fa08c87667717e5dcfa55d
• https://git.kernel.org/stable/c/1fea5ff0eb4aa7e951bb3d380248566c473aa377
• https://git.kernel.org/stable/c/a5cdd2407dd890f741f59b8367e4c6c101cce154
• https://git.kernel.org/stable/c/2dc2fffc704a4365cae1aae078ba62223aaeff93
• https://git.kernel.org/stable/c/295dd295e2137e10e9a5b1891d97e0f08de76f03