bpf: Preserve special fields in recycled rhtab elements

Summary

In the Linux kernel, the following vulnerability has been resolved: bpf: Preserve special fields in recycled rhtab elements rhtab_map_update_elem() initializes special fields after obtaining an element from bpf_mem_cache_alloc(). The allocator can return a fresh, zeroed unit, or recycle one from its RCU-pending lists before the registered destructor has run. A BPF program can retain a map-value pointer after deleting its element and initialize and arm a timer through that pointer. If the deleted unit is recycled, check_and_init_map_value() clears the only pointer to the timer. Neither a later deletion nor rhtab_mem_dtor() can then cancel it, and the callback can run with its key and value pointing into freed memory. Do not reinitialize special fields on insertion. Fresh allocator units are already zeroed. For recycled units, the special fields are ownership state that must remain visible to the eventual destructor. copy_map_value() already skips those fields, matching the non-preallocated hash-map path and the lifecycle established by commit 275c30bcee66 ("bpf: Don't reinit map value in prealloc_lru_pop"). [ kkd: Split out the fix and rewrote the commit log ]

Timeline

1. Sep 25, 2026, 10:23 AM UTCCVE published
2. Oct 19, 2026, 9:12 AM UTCRecord last updated

Affected versions

• Linux Linux

  From 6905f8601298ecd2d1932a4b4849bf265201118e · fixed in 6a5266b8288216b86602ff687d528abfb066dfd8; From 6905f8601298ecd2d1932a4b4849bf265201118e · fixed in 5df46ddcb7b36878c1b691e9057a0509042a2567

• Linux Linux

  7.2

• KernelLinux

  From 7.2.0 · fixed in 7.2.7

References 2