releases/6.6.14/bpf-guard-stack-limits-against-32bit-overflow.patch

From 67f3b3b07b9bc5d545c0e8bf1bb3c910fe1836b6 Mon Sep 17 00:00:00 2001
From: Sasha Levin <sashal@kernel.org>
Date: Wed, 6 Dec 2023 23:11:50 -0500
Subject: bpf: Guard stack limits against 32bit overflow

From: Andrei Matei <andreimatei1@gmail.com>

[ Upstream commit 1d38a9ee81570c4bd61f557832dead4d6f816760 ]

This patch promotes the arithmetic around checking stack bounds to be
done in the 64-bit domain, instead of the current 32bit. The arithmetic
implies adding together a 64-bit register with a int offset. The
register was checked to be below 1<<29 when it was variable, but not
when it was fixed. The offset either comes from an instruction (in which
case it is 16 bit), from another register (in which case the caller
checked it to be below 1<<29 [1]), or from the size of an argument to a
kfunc (in which case it can be a u32 [2]). Between the register being
inconsistently checked to be below 1<<29, and the offset being up to an
u32, it appears that we were open to overflowing the `int`s which were
currently used for arithmetic.

[1] https://github.com/torvalds/linux/blob/815fb87b753055df2d9e50f6cd80eb10235fe3e9/kernel/bpf/verifier.c#L7494-L7498
[2] https://github.com/torvalds/linux/blob/815fb87b753055df2d9e50f6cd80eb10235fe3e9/kernel/bpf/verifier.c#L11904

Reported-by: Andrii Nakryiko <andrii.nakryiko@gmail.com>
Signed-off-by: Andrei Matei <andreimatei1@gmail.com>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Acked-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/20231207041150.229139-4-andreimatei1@gmail.com
Stable-dep-of: 6b4a64bafd10 ("bpf: Fix accesses to uninit stack slots")
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 kernel/bpf/verifier.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index 76834ecc59a9..47599505cdf8 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -6371,7 +6371,7 @@ static int check_ptr_to_map_access(struct bpf_verifier_env *env,
  * The minimum valid offset is -MAX_BPF_STACK for writes, and
  * -state->allocated_stack for reads.
  */
-static int check_stack_slot_within_bounds(int off,
+static int check_stack_slot_within_bounds(s64 off,
 					  struct bpf_func_state *state,
 					  enum bpf_access_type t)
 {
@@ -6400,7 +6400,7 @@ static int check_stack_access_within_bounds(
 	struct bpf_reg_state *regs = cur_regs(env);
 	struct bpf_reg_state *reg = regs + regno;
 	struct bpf_func_state *state = func(env, reg);
-	int min_off, max_off;
+	s64 min_off, max_off;
 	int err;
 	char *err_extra;
 
@@ -6413,7 +6413,7 @@ static int check_stack_access_within_bounds(
 		err_extra = " write to";
 
 	if (tnum_is_const(reg->var_off)) {
-		min_off = reg->var_off.value + off;
+		min_off = (s64)reg->var_off.value + off;
 		max_off = min_off + access_size;
 	} else {
 		if (reg->smax_value >= BPF_MAX_VAR_OFF ||
-- 
2.43.0