From 5df0ff8ae139e1bd09041eb4e2374e77a3dee2d4 Mon Sep 17 00:00:00 2001 From: Yonghong Song Date: Mon, 12 Aug 2024 14:48:47 -0700 Subject: [PATCH] bpf: Fix a kernel verifier crash in stacksafe() BugLink: https://bugs.launchpad.net/bugs/2084005 commit bed2eb964c70b780fb55925892a74f26cb590b25 upstream. Daniel Hodges reported a kernel verifier crash when playing with sched-ext. Further investigation shows that the crash is due to invalid memory access in stacksafe(). More specifically, it is the following code: if (exact != NOT_EXACT && old->stack[spi].slot_type[i % BPF_REG_SIZE] != cur->stack[spi].slot_type[i % BPF_REG_SIZE]) return false; The 'i' iterates old->allocated_stack. If cur->allocated_stack < old->allocated_stack the out-of-bound access will happen. To fix the issue add 'i >= cur->allocated_stack' check such that if the condition is true, stacksafe() should fail. Otherwise, cur->stack[spi].slot_type[i % BPF_REG_SIZE] memory access is legal. Fixes: 2793a8b015f7 ("bpf: exact states comparison for iterator convergence checks") Cc: Eduard Zingerman Reported-by: Daniel Hodges Acked-by: Eduard Zingerman Signed-off-by: Yonghong Song Link: https://lore.kernel.org/r/20240812214847.213612-1-yonghong.song@linux.dev Signed-off-by: Alexei Starovoitov [ shung-hsi.yu: "exact" variable is bool instead enum because commit 4f81c16f50ba ("bpf: Recognize that two registers are safe when their ranges match") is not present. ] Signed-off-by: Shung-Hsi Yu Signed-off-by: Greg Kroah-Hartman Signed-off-by: Koichiro Den Signed-off-by: Stefan Bader --- kernel/bpf/verifier.c | 5 +++-- 1 file changed, 3 insertions(+), 2 deletions(-) diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c index ee5e8d04f560..ba8a4322aa5b 100644 --- a/kernel/bpf/verifier.c +++ b/kernel/bpf/verifier.c @@ -16499,8 +16499,9 @@ static bool stacksafe(struct bpf_verifier_env *env, struct bpf_func_state *old, spi = i / BPF_REG_SIZE; if (exact && - old->stack[spi].slot_type[i % BPF_REG_SIZE] != - cur->stack[spi].slot_type[i % BPF_REG_SIZE]) + (i >= cur->allocated_stack || + old->stack[spi].slot_type[i % BPF_REG_SIZE] != + cur->stack[spi].slot_type[i % BPF_REG_SIZE])) return false; if (!(old->stack[spi].spilled_ptr.live & REG_LIVE_READ) && !exact) {