From: "Mickaël Salaün" <mic@digikod.net>
To: linux-kernel@vger.kernel.org
Cc: "Mickaël Salaün" <mic@digikod.net>,
"Alexei Starovoitov" <ast@fb.com>,
"Daniel Borkmann" <daniel@iogearbox.net>,
"David S . Miller" <davem@davemloft.net>,
"Kees Cook" <keescook@chromium.org>,
"Martin KaFai Lau" <kafai@fb.com>,
netdev@vger.kernel.org, "Alexei Starovoitov" <ast@kernel.org>
Subject: [PATCH net-next v1 2/2] bpf: Extend check_uarg_tail_zero() checks
Date: Mon, 7 Aug 2017 18:36:05 +0200 [thread overview]
Message-ID: <20170807163605.14194-2-mic@digikod.net> (raw)
In-Reply-To: <20170807163605.14194-1-mic@digikod.net>
The function check_uarg_tail_zero() was created from bpf(2) for
BPF_OBJ_GET_INFO_BY_FD without taking the access_ok() nor the PAGE_SIZE
checks. Make this checks more generally available while unlikely to be
triggered, extend the memory range check and add an explanation
including why the ToCToU should not be a security concern.
Signed-off-by: Mickaël Salaün <mic@digikod.net>
Cc: Alexei Starovoitov <ast@kernel.org>
Cc: Daniel Borkmann <daniel@iogearbox.net>
Cc: David S. Miller <davem@davemloft.net>
Cc: Kees Cook <keescook@chromium.org>
Cc: Martin KaFai Lau <kafai@fb.com>
Link: https://lkml.kernel.org/r/CAGXu5j+vRGFvJZmjtAcT8Hi8B+Wz0e1b6VKYZHfQP_=DXzC4CQ@mail.gmail.com
---
kernel/bpf/syscall.c | 26 +++++++++++++++-----------
1 file changed, 15 insertions(+), 11 deletions(-)
diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
index c653ee0bd162..b884fdc371e0 100644
--- a/kernel/bpf/syscall.c
+++ b/kernel/bpf/syscall.c
@@ -48,6 +48,15 @@ static const struct bpf_map_ops * const bpf_map_types[] = {
#undef BPF_MAP_TYPE
};
+/*
+ * If we're handed a bigger struct than we know of, ensure all the unknown bits
+ * are 0 - i.e. new user-space does not rely on any kernel feature extensions
+ * we dont know about yet.
+ *
+ * There is a ToCToU between this function call and the following
+ * copy_from_user() call. However, this should not be a concern since this
+ * function is meant to be a future-proofing of bits.
+ */
static int check_uarg_tail_zero(void __user *uaddr,
size_t expected_size,
size_t actual_size)
@@ -57,6 +66,12 @@ static int check_uarg_tail_zero(void __user *uaddr,
unsigned char val;
int err;
+ if (unlikely(!access_ok(VERIFY_READ, uaddr, actual_size)))
+ return -EFAULT;
+
+ if (unlikely(actual_size > PAGE_SIZE)) /* silly large */
+ return -E2BIG;
+
if (actual_size <= expected_size)
return 0;
@@ -1393,17 +1408,6 @@ SYSCALL_DEFINE3(bpf, int, cmd, union bpf_attr __user *, uattr, unsigned int, siz
if (!capable(CAP_SYS_ADMIN) && sysctl_unprivileged_bpf_disabled)
return -EPERM;
- if (!access_ok(VERIFY_READ, uattr, 1))
- return -EFAULT;
-
- if (size > PAGE_SIZE) /* silly large */
- return -E2BIG;
-
- /* If we're handed a bigger struct than we know of,
- * ensure all the unknown bits are 0 - i.e. new
- * user-space does not rely on any kernel feature
- * extensions we dont know about yet.
- */
err = check_uarg_tail_zero(uattr, sizeof(attr), size);
if (err)
return err;
--
2.13.3
next prev parent reply other threads:[~2017-08-07 16:36 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-08-07 16:36 [PATCH net-next v1 1/2] bpf: Move check_uarg_tail_zero() upward Mickaël Salaün
2017-08-07 16:36 ` Mickaël Salaün [this message]
2017-08-07 18:34 ` [PATCH net-next v1 2/2] bpf: Extend check_uarg_tail_zero() checks Daniel Borkmann
2017-08-07 18:24 ` [PATCH net-next v1 1/2] bpf: Move check_uarg_tail_zero() upward Daniel Borkmann
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