From 5df46ddcb7b36878c1b691e9057a0509042a2567 Mon Sep 17 00:00:00 2001 From: Yuan Chen Date: Fri, 4 Sep 2026 12:41:52 +0200 Subject: [PATCH] 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"). Fixes: 6905f8601298 ("bpf: Allow special fields in resizable hashtab") Reported-by: Nicholas Carlini Suggested-by: Nicholas Carlini Signed-off-by: Yuan Chen [ kkd: Split out the fix and rewrote the commit log ] Signed-off-by: Kumar Kartikeya Dwivedi Link: https://lore.kernel.org/r/20260904104203.345917-2-memxor@gmail.com Signed-off-by: Alexei Starovoitov --- kernel/bpf/hashtab.c | 1 - 1 file changed, 1 deletion(-) diff --git a/kernel/bpf/hashtab.c b/kernel/bpf/hashtab.c index e89fde188389..527cc5716ee8 100644 --- a/kernel/bpf/hashtab.c +++ b/kernel/bpf/hashtab.c @@ -3070,7 +3070,6 @@ static long rhtab_map_update_elem(struct bpf_map *map, void *key, void *value, u memcpy(elem->data, key, map->key_size); copy_map_value(map, rhtab_elem_value(elem, map->key_size), value); - check_and_init_map_value(map, rhtab_elem_value(elem, map->key_size)); /* Prevent deadlock for NMI programs attempting to take bucket lock */ bpf_disable_instrumentation();