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From:   Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To:     linux-kernel@vger.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        stable@vger.kernel.org, Kuniyuki Iwashima <kuniyu@amazon.com>,
        Daniel Borkmann <daniel@iogearbox.net>,
        Sasha Levin <sashal@kernel.org>
Subject: [PATCH 5.19 019/155] bpf: Fix a data-race around bpf_jit_limit.
Date:   Tue,  6 Sep 2022 15:29:27 +0200
Message-Id: <20220906132830.235883991@linuxfoundation.org>
In-Reply-To: <20220906132829.417117002@linuxfoundation.org>
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From: Kuniyuki Iwashima <kuniyu@amazon.com>

[ Upstream commit 0947ae1121083d363d522ff7518ee72b55bd8d29 ]

While reading bpf_jit_limit, it can be changed concurrently via sysctl,
WRITE_ONCE() in __do_proc_doulongvec_minmax(). The size of bpf_jit_limit
is long, so we need to add a paired READ_ONCE() to avoid load-tearing.

Fixes: ede95a63b5e8 ("bpf: add bpf_jit_limit knob to restrict unpriv allocations")
Signed-off-by: Kuniyuki Iwashima <kuniyu@amazon.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Link: https://lore.kernel.org/bpf/20220823215804.2177-1-kuniyu@amazon.com
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 kernel/bpf/core.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/bpf/core.c b/kernel/bpf/core.c
index fb6bd57228a84..cf44ff50b1f23 100644
--- a/kernel/bpf/core.c
+++ b/kernel/bpf/core.c
@@ -1005,7 +1005,7 @@ pure_initcall(bpf_jit_charge_init);
 
 int bpf_jit_charge_modmem(u32 size)
 {
-	if (atomic_long_add_return(size, &bpf_jit_current) > bpf_jit_limit) {
+	if (atomic_long_add_return(size, &bpf_jit_current) > READ_ONCE(bpf_jit_limit)) {
 		if (!bpf_capable()) {
 			atomic_long_sub(size, &bpf_jit_current);
 			return -EPERM;
-- 
2.35.1