netlink: avoid hashing the network namespace pointer
Impact
In the Linux kernel, the following vulnerability has been resolved:
Source excerpt · LinuxAffected packages
Affected products
Vendor version evidence. Product records are separate from automatic dependency matching.
Linux · Linux
Other versions: unaffected
| Version / range | Source status |
|---|---|
| c428ecd1a21f1457ca3beb4df71b8a079c410e41 to before bdd55b8a8acbf6b4840ab420eb6a63774bf4593b | affected |
| c428ecd1a21f1457ca3beb4df71b8a079c410e41 to before 078deff25f8a849ecd1c3fe17b1e473b1cf44f28 | affected |
| c428ecd1a21f1457ca3beb4df71b8a079c410e41 to before f88bb3606e4bd11ee035b682cddc2999e604609a | affected |
Linux · Linux
Other versions: affected
| Version / range | Source status |
|---|---|
| 4.1 | affected |
| 0 to before 4.1 | unaffected |
| 6.18.59 through 6.18.* (inclusive) | unaffected |
| 7.2.13 through 7.2.* (inclusive) | unaffected |
| 7.3 through * (inclusive) | unaffected |
Original source description
In the Linux kernel, the following vulnerability has been resolved:
netlink: avoid hashing the network namespace pointer
The netlink rhashtable key includes a raw struct net pointer and a user-controlled port ID. Both /proc/net/netlink and socket diagnostics expose the table's bucket order. By binding and rebinding chosen NETLINK_USERSOCK port IDs, an unprivileged reader can distinguish equal buckets and recover the low bits of the Jenkins hash. Its 32-bit seed and the limited set of kernel-image slides can then be searched offline to recover the address of init_net.
Use the namespace's unique, non-address net_cookie in the comparison key instead. It is assigned before the per-net initializers run and remains unchanged for the namespace's lifetime. The lookup key and object hash are still built by netlink_compare_arg_init(), keeping lookup, insertion, removal and rehashing consistent while preserving namespace separation. Neither public table walker needs to change.
Reading the socket's namespace cookie in netlink_compare() is safe under RCU, including during namespace teardown. netlink_release() removes the socket from the hash table and defers its final put with call_rcu(). cleanup_net() runs the per-net exit methods and waits for outstanding RCU callbacks with rcu_barrier() before freeing namespace storage.
Unlike ns.ns_id, net_cookie is also available and initialized during setup_net() in older stable kernels, making the change straightforward to backport to v5.15 and later.