Linux vulnerability

What happened

In the Linux kernel, the following vulnerability has been resolved: net: add proper RCU protection to /proc/net/ptype Yin Fengwei reported an RCU stall in ptype_seq_show() and provided a patch. Real issue is that ptype_seq_next() and ptype_seq_show() violate RCU rules. ptype_seq_show() runs under rcu_read_lock(), and reads pt->dev to get device name without any barrier. At the same time, concurrent writers can remove a packet_type structure (which is correctly freed after an RCU grace period) and clear pt->dev without an RCU grace period. Define ptype_iter_state to carry a dev pointer along seq_net_private: struct ptype_iter_state { struct seq_net_private p; struct net_device *dev; // added in this patch }; We need to record the device pointer in ptype_get_idx() and ptype_seq_next() so that ptype_seq_show() is safe against concurrent pt->dev changes. We also need to add full RCU protection in ptype_seq_next(). (Missing READ_ONCE() when reading list.next values) Many thanks to Dong Chenchen for providing a repro.

Affected versions

Linux: 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 through before e974a10a52618f7f57a4bce173a0ed96acd4e5dc (git); 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 through before 002a73470b56848e4c81efeaaedd471e92d66d8d (git); 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 through before dcefd3f0b9ed8288654c75254bdcee8e1085e861 (git); 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 through before 589a530ae44d0c80f523fcfd1a15af8087f27d35 (git); 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 through before f613e8b4afea0cd17c7168e8b00e25bc8d33175d (git); 2.6.12; V3.1.6 through before * (custom) Fixed: See vendor advisory.

Why it matters

Review the vendor advisory and exposure of the affected product to determine operational impact.

Detection & mitigation

• Apply vendor-provided updates or mitigations.
• Review affected product exposure and access logs.