Description

In the Linux kernel, the following vulnerability has been resolved: net: rtnetlink: zero ifla_vf_broadcast to avoid stack infoleak in rtnl_fill_vfinfo rtnl_fill_vfinfo() declares struct ifla_vf_broadcast on the stack without initialisation: struct ifla_vf_broadcast vf_broadcast; The struct contains a single fixed 32-byte field: /* include/uapi/linux/if_link.h */ struct ifla_vf_broadcast { __u8 broadcast[32]; }; The function then copies dev->broadcast into it using dev->addr_len as the length: memcpy(vf_broadcast.broadcast, dev->broadcast, dev->addr_len); On Ethernet devices (the overwhelming majority of SR-IOV NICs) dev->addr_len is 6, so only the first 6 bytes of broadcast[] are written. The remaining 26 bytes retain whatever was previously on the kernel stack. The full struct is then handed to userspace via: nla_put(skb, IFLA_VF_BROADCAST, sizeof(vf_broadcast), &vf_broadcast) leaking up to 26 bytes of uninitialised kernel stack per VF per RTM_GETLINK request, repeatable. The other vf_* structs in the same function are explicitly zeroed for exactly this reason - see the memset() calls for ivi, vf_vlan_info, node_guid and port_guid a few lines above. vf_broadcast was simply missed when it was added. Reachability: any unprivileged local process can open AF_NETLINK / NETLINK_ROUTE without capabilities and send RTM_GETLINK with an IFLA_EXT_MASK attribute carrying RTEXT_FILTER_VF. The kernel walks each VF and emits IFLA_VF_BROADCAST, leaking 26 bytes of stack per VF per request. Stack residue at this call site can include return addresses and transient sensitive data; KASAN with stack instrumentation, or KMSAN, will flag the nla_put() when reproduced. Zero the on-stack struct before the partial memcpy, matching the existing pattern used for the other vf_* structs in the same function.

References 8

• git.kernel.org https://git.kernel.org/stable/c/0653c0516234c8258975d268a749115fc0f0ff00
• git.kernel.org https://git.kernel.org/stable/c/14271b401ec6a4bf0d88054106fc2956084717e1
• git.kernel.org https://git.kernel.org/stable/c/38bcc21f52246badb3154b6158dcb381d98de011
• git.kernel.org https://git.kernel.org/stable/c/4b9e327991815e128ad3af75c3a04630a63ce3e0
• git.kernel.org https://git.kernel.org/stable/c/a44fbb631cba646532f3948636626f81717365a7
• git.kernel.org https://git.kernel.org/stable/c/c5b1b92ab7eff1a6e8c507ddde6fd02fabd0cfa8
• git.kernel.org https://git.kernel.org/stable/c/cccce3190ba4356432b9f22369b56123d3d89f0d
• git.kernel.org https://git.kernel.org/stable/c/fbe0e6197225e6a83cf113a67a4b425f8de0bcd5

Remediation