From: Yonghong Song yonghong.song@linux.dev
[ Upstream commit bed2eb964c70b780fb55925892a74f26cb590b25 ]
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 eddyz87@gmail.com Reported-by: Daniel Hodges hodgesd@meta.com Acked-by: Eduard Zingerman eddyz87@gmail.com Signed-off-by: Yonghong Song yonghong.song@linux.dev Link: https://lore.kernel.org/r/20240812214847.213612-1-yonghong.song@linux.dev Signed-off-by: Alexei Starovoitov ast@kernel.org Signed-off-by: Shung-Hsi Yu shung-hsi.yu@suse.com --- I see this patch itself was already picked up[1] by Sasha. This thread additional includes the associated selftest that was sent in the same series (not entirely sure if backporting selftest goes against the stable backporting rule though).
1: https://git.kernel.org/pub/scm/linux/kernel/git/stable/stable-queue.git/comm... --- 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 a8845cc299fe..521bd7efae03 100644 --- a/kernel/bpf/verifier.c +++ b/kernel/bpf/verifier.c @@ -16881,8 +16881,9 @@ static bool stacksafe(struct bpf_verifier_env *env, struct bpf_func_state *old, spi = i / BPF_REG_SIZE;
if (exact != NOT_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)