[PATCH v3 bpf] bpf: Fix a data-race around bpf_jit_limit.

[PATCH v3 bpf] bpf: Fix a data-race around bpf_jit_limit.

[Kuniyuki Iwashima]

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>
---
v3:
  * Update changelog to clarify paired WRITE_ONCE() and motivation
    as load-tearing.

v2: https://lore.kernel.org/netdev/20220823181247.90349-1-kuniyu@amazon.com/
  * Drop other 3 patches (No change for this patch)

v1: https://lore.kernel.org/bpf/20220818042339.82992-1-kuniyu@amazon.com/
---
 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 c1e10d088dbb..3d9eb3ae334c 100644
--- a/kernel/bpf/core.c
+++ b/kernel/bpf/core.c
@@ -971,7 +971,7 @@ 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;
-- 
2.30.2

Re: [PATCH v3 bpf] bpf: Fix a data-race around bpf_jit_limit.

[patchwork-bot+netdevbpf]

Hello:

This patch was applied to bpf/bpf.git (master)
by Daniel Borkmann <daniel@iogearbox.net>:

On Tue, 23 Aug 2022 14:58:04 -0700 you wrote:
> 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>
> 
> [...]

Here is the summary with links:
  - [v3,bpf] bpf: Fix a data-race around bpf_jit_limit.
    https://git.kernel.org/bpf/bpf/c/0947ae112108

You are awesome, thank you!
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