From b5a71cb2db6d84ac0042549dcec266b18429d41e Mon Sep 17 00:00:00 2001 From: Yiyang Chen Date: Fri, 17 Jul 2026 12:53:47 +0000 Subject: [PATCH] bpf: Reject arena frees below the arena base bpf_arena_free_pages() accepts scalar arena addresses. The runtime masks the address to the low 32 bits and reconstructs a full user address from the arena base before returning the range to the arena free tree. When the scalar value is below the low 32 bits of the arena base, full_uaddr falls below user_vm_start. The existing upper-end clipping then turns this into an out-of-range free-tree offset. A later allocation can reuse that offset and return an address below the arena mapping. Reject such frees before computing the clipped range. Fixes: 317460317a02a ("bpf: Introduce bpf_arena.") Signed-off-by: Yiyang Chen Reviewed-by: Emil Tsalapatis Link: https://lore.kernel.org/bpf/20260717-c10-031-public-bpf-next-v2-b4-v2-1-54b555443a7c@mails.tsinghua.edu.cn Signed-off-by: Kumar Kartikeya Dwivedi --- kernel/bpf/arena.c | 2 ++ 1 file changed, 2 insertions(+) diff --git a/kernel/bpf/arena.c b/kernel/bpf/arena.c index f046e878f7ae..34f023a537fe 100644 --- a/kernel/bpf/arena.c +++ b/kernel/bpf/arena.c @@ -858,6 +858,8 @@ static void arena_free_pages(struct bpf_arena *arena, long uaddr, long page_cnt, uaddr &= PAGE_MASK; kaddr = bpf_arena_get_kern_vm_start(arena) + uaddr; full_uaddr = clear_lo32(arena->user_vm_start) + uaddr; + if (full_uaddr < arena->user_vm_start) + return; uaddr_end = min(arena->user_vm_end, full_uaddr + (page_cnt << PAGE_SHIFT)); if (full_uaddr >= uaddr_end) return;