From 75b0a6db4300e4c2c9e97a0848deaa7acfb42fb7 Mon Sep 17 00:00:00 2001 From: Hui Su Date: Thu, 13 Aug 2026 23:51:33 +0800 Subject: bpf: Fix percpu map update indexing with sparse CPU IDs Per-CPU array, hash, and cgroup storage map updates without BPF_F_CPU or BPF_F_ALL_CPUS use a value buffer whose per-CPU slots are packed in possible-CPU order. The buffer is sized as: round_up(value_size, 8) * num_possible_cpus() The update paths iterate over possible CPUs, but use the logical CPU ID to calculate the source offset: value + size * cpu This only works when possible CPU IDs are contiguous starting at zero. For example, with a possible CPU mask of 0,2-3, the buffer contains three slots corresponding to CPUs 0, 2, and 3. CPU2 is therefore expected to use slot 1 and CPU3 slot 2. Instead, the current code uses slots 2 and 3 respectively, causing incorrect per-CPU values and an out-of-bounds read from the update buffer for CPU3. The corresponding lookup paths already use a dense offset while iterating over possible CPUs. Do the same for the array, hash, and cgroup storage update paths, advancing the source offset once for each possible CPU. BPF_F_ALL_CPUS continues to use the same value for every CPU. Fixes: 8eb76cb03f0f ("bpf: Add BPF_F_CPU and BPF_F_ALL_CPUS flags support for percpu_array maps") Fixes: c6936161fd55 ("bpf: Add BPF_F_CPU and BPF_F_ALL_CPUS flags support for percpu_hash and lru_percpu_hash maps") Fixes: 47c79f05aa0d ("bpf: Add BPF_F_CPU and BPF_F_ALL_CPUS flags support for percpu_cgroup_storage maps") Signed-off-by: Hui Su Signed-off-by: Andrii Nakryiko Acked-by: Leon Hwang Link: https://lore.kernel.org/bpf/20260813155131.1022745-3-sh_def@163.com --- kernel/bpf/arraymap.c | 5 +++-- 1 file changed, 3 insertions(+), 2 deletions(-) (limited to 'kernel/bpf/arraymap.c') diff --git a/kernel/bpf/arraymap.c b/kernel/bpf/arraymap.c index ef315b168b29..0ce26b538075 100644 --- a/kernel/bpf/arraymap.c +++ b/kernel/bpf/arraymap.c @@ -436,7 +436,7 @@ int bpf_percpu_array_update(struct bpf_map *map, void *key, void *value, void __percpu *pptr; void *ptr, *val; u32 size; - int cpu; + int cpu, off = 0; if (unlikely((map_flags & BPF_F_LOCK) || (u32)map_flags > BPF_F_ALL_CPUS)) /* unknown flags */ @@ -468,9 +468,10 @@ int bpf_percpu_array_update(struct bpf_map *map, void *key, void *value, } for_each_possible_cpu(cpu) { ptr = per_cpu_ptr(pptr, cpu); - val = (map_flags & BPF_F_ALL_CPUS) ? value : value + size * cpu; + val = (map_flags & BPF_F_ALL_CPUS) ? value : value + off; copy_map_value(map, ptr, val); bpf_obj_cancel_fields(map, ptr); + off += size; } unlock: rcu_read_unlock(); -- cgit v1.2.3