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From:   Christian Brauner <christian.brauner@ubuntu.com>
To:     Alexei Starovoitov <ast@kernel.org>,
        Daniel Borkmann <daniel@iogearbox.net>, bpf@vger.kernel.org
Cc:     Martin KaFai Lau <kafai@fb.com>, Song Liu <songliubraving@fb.com>,
        Yonghong Song <yhs@fb.com>, netdev@vger.kernel.org,
        linux-kernel@vger.kernel.org,
        Christian Brauner <christian.brauner@ubuntu.com>
Subject: [PATCH 2/3] bpf: use copy_struct_from_user() in bpf_prog_get_info_by_fd()
Date:   Wed,  9 Oct 2019 18:09:06 +0200
Message-Id: <20191009160907.10981-3-christian.brauner@ubuntu.com>
In-Reply-To: <20191009160907.10981-1-christian.brauner@ubuntu.com>
References: <20191009160907.10981-1-christian.brauner@ubuntu.com>
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In v5.4-rc2 we added a new helper (cf. [1]) copy_struct_from_user().
This helper is intended for all codepaths that copy structs from
userspace that are versioned by size. bpf_prog_get_info_by_fd() does
exactly what copy_struct_from_user() is doing.
Note that copy_struct_from_user() is calling min() already. So
technically, the min_t() call could go. But the info_len is used further
below so leave it.

[1]: f5a1a536fa14 ("lib: introduce copy_struct_from_user() helper")
Signed-off-by: Christian Brauner <christian.brauner@ubuntu.com>
---
 kernel/bpf/syscall.c | 7 ++-----
 1 file changed, 2 insertions(+), 5 deletions(-)

diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
index 78790778f101..6f4f9097b1fe 100644
--- a/kernel/bpf/syscall.c
+++ b/kernel/bpf/syscall.c
@@ -2312,13 +2312,10 @@ static int bpf_prog_get_info_by_fd(struct bpf_prog *prog,
 	u32 ulen;
 	int err;
 
-	err = bpf_check_uarg_tail_zero(uinfo, sizeof(info), info_len);
+	info_len = min_t(u32, sizeof(info), info_len);
+	err = copy_struct_from_user(&info, sizeof(info), uinfo, info_len);
 	if (err)
 		return err;
-	info_len = min_t(u32, sizeof(info), info_len);
-
-	if (copy_from_user(&info, uinfo, info_len))
-		return -EFAULT;
 
 	info.type = prog->type;
 	info.id = prog->aux->id;
-- 
2.23.0