netdev - [PATCH v3 2/3] bpf: use copy_struct_from_user() in bpf_prog_get_info_by

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Message-Id: <20191016034432.4418-3-christian.brauner@ubuntu.com>
Date:   Wed, 16 Oct 2019 05:44:31 +0200
From:   Christian Brauner <christian.brauner@...ntu.com>
To:     christian.brauner@...ntu.com
Cc:     ast@...nel.org, bpf@...r.kernel.org, daniel@...earbox.net,
        kafai@...com, linux-kernel@...r.kernel.org, netdev@...r.kernel.org,
        songliubraving@...com, yhs@...com, Aleksa Sarai <cyphar@...har.com>
Subject: [PATCH v3 2/3] bpf: use copy_struct_from_user() in bpf_prog_get_info_by_fd()

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")
Cc: Alexei Starovoitov <ast@...nel.org>
Cc: Daniel Borkmann <daniel@...earbox.net>
Cc: bpf@...r.kernel.org
Acked-by: Aleksa Sarai <cyphar@...har.com>
Signed-off-by: Christian Brauner <christian.brauner@...ntu.com>
---
/* v1 */
Link: https://lore.kernel.org/r/20191009160907.10981-3-christian.brauner@ubuntu.com

/* v2 */
Link: https://lore.kernel.org/r/20191016004138.24845-3-christian.brauner@ubuntu.com
- Alexei Starovoitov <ast@...nel.org>:
  - remove unneeded initialization

/* v3 */
unchanged
---
 kernel/bpf/syscall.c | 9 +++------
 1 file changed, 3 insertions(+), 6 deletions(-)

diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
index 40edcaeccd71..151447f314ca 100644
--- a/kernel/bpf/syscall.c
+++ b/kernel/bpf/syscall.c
@@ -2306,20 +2306,17 @@ static int bpf_prog_get_info_by_fd(struct bpf_prog *prog,
 				   union bpf_attr __user *uattr)
 {
 	struct bpf_prog_info __user *uinfo = u64_to_user_ptr(attr->info.info);
-	struct bpf_prog_info info = {};
+	struct bpf_prog_info info;
 	u32 info_len = attr->info.info_len;
 	struct bpf_prog_stats stats;
 	char __user *uinsns;
 	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