From: Yonghong Song <yonghong.song@xxxxxxxxx>
[ 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@xxxxxxxxx>
Reported-by: Daniel Hodges <hodgesd@xxxxxxxx>
Acked-by: Eduard Zingerman <eddyz87@xxxxxxxxx>
Signed-off-by: Yonghong Song <yonghong.song@xxxxxxxxx>
Link: https://lore.kernel.org/r/20240812214847.213612-1-yonghong.song@xxxxxxxxx
Signed-off-by: Alexei Starovoitov <ast@xxxxxxxxxx>
Signed-off-by: Shung-Hsi Yu <shung-hsi.yu@xxxxxxxx>
---
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/commit/queue-6.10/bpf-fix-a-kernel-verifier-crash-in-stacksafe.patch?id=e1b8b4a2ab5985f048c5e4ba7575deaa7bb65df7
---
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)
--
2.46.0
