From: Stanislav Fomichev <sdf@google.com>
Date: Tue, 16 Jun 2020 18:04:15 -0700
Subject: selftests/bpf: Make sure optvals > PAGE_SIZE are bypassed
Patch-mainline: v5.8-rc3
Git-commit: a0cb12b03132befbdb29d835ca330c18792e8134
References: bsc#1155518
We are relying on the fact, that we can pass > sizeof(int) optvals
to the SOL_IP+IP_FREEBIND option (the kernel will take first 4 bytes).
In the BPF program we check that we can only touch PAGE_SIZE bytes,
but the real optlen is PAGE_SIZE * 2. In both cases, we override it to
some predefined value and trim the optlen.
Also, let's modify exiting IP_TOS usecase to test optlen=0 case
where BPF program just bypasses the data as is.
Signed-off-by: Stanislav Fomichev <sdf@google.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/20200617010416.93086-2-sdf@google.com
Acked-by: Gary Lin <glin@suse.com>
---
tools/testing/selftests/bpf/progs/sockopt_sk.c | 54 ++++++++++++++++++++++++-
1 file changed, 52 insertions(+), 2 deletions(-)
--- a/tools/testing/selftests/bpf/progs/sockopt_sk.c
+++ b/tools/testing/selftests/bpf/progs/sockopt_sk.c
@@ -6,6 +6,10 @@
char _license[] SEC("license") = "GPL";
__u32 _version SEC("version") = 1;
+#ifndef PAGE_SIZE
+#define PAGE_SIZE 4096
+#endif
+
#define SOL_CUSTOM 0xdeadbeef
struct sockopt_sk {
@@ -26,12 +30,14 @@ int _getsockopt(struct bpf_sockopt *ctx)
__u8 *optval = ctx->optval;
struct sockopt_sk *storage;
- if (ctx->level == SOL_IP && ctx->optname == IP_TOS)
+ if (ctx->level == SOL_IP && ctx->optname == IP_TOS) {
/* Not interested in SOL_IP:IP_TOS;
* let next BPF program in the cgroup chain or kernel
* handle it.
*/
+ ctx->optlen = 0; /* bypass optval>PAGE_SIZE */
return 1;
+ }
if (ctx->level == SOL_SOCKET && ctx->optname == SO_SNDBUF) {
/* Not interested in SOL_SOCKET:SO_SNDBUF;
@@ -41,6 +47,26 @@ int _getsockopt(struct bpf_sockopt *ctx)
return 1;
}
+ if (ctx->level == SOL_IP && ctx->optname == IP_FREEBIND) {
+ if (optval + 1 > optval_end)
+ return 0; /* EPERM, bounds check */
+
+ ctx->retval = 0; /* Reset system call return value to zero */
+
+ /* Always export 0x55 */
+ optval[0] = 0x55;
+ ctx->optlen = 1;
+
+ /* Userspace buffer is PAGE_SIZE * 2, but BPF
+ * program can only see the first PAGE_SIZE
+ * bytes of data.
+ */
+ if (optval_end - optval != PAGE_SIZE)
+ return 0; /* EPERM, unexpected data size */
+
+ return 1;
+ }
+
if (ctx->level != SOL_CUSTOM)
return 0; /* EPERM, deny everything except custom level */
@@ -71,12 +97,14 @@ int _setsockopt(struct bpf_sockopt *ctx)
__u8 *optval = ctx->optval;
struct sockopt_sk *storage;
- if (ctx->level == SOL_IP && ctx->optname == IP_TOS)
+ if (ctx->level == SOL_IP && ctx->optname == IP_TOS) {
/* Not interested in SOL_IP:IP_TOS;
* let next BPF program in the cgroup chain or kernel
* handle it.
*/
+ ctx->optlen = 0; /* bypass optval>PAGE_SIZE */
return 1;
+ }
if (ctx->level == SOL_SOCKET && ctx->optname == SO_SNDBUF) {
/* Overwrite SO_SNDBUF value */
@@ -89,6 +117,28 @@ int _setsockopt(struct bpf_sockopt *ctx)
return 1;
}
+
+ if (ctx->level == SOL_IP && ctx->optname == IP_FREEBIND) {
+ /* Original optlen is larger than PAGE_SIZE. */
+ if (ctx->optlen != PAGE_SIZE * 2)
+ return 0; /* EPERM, unexpected data size */
+
+ if (optval + 1 > optval_end)
+ return 0; /* EPERM, bounds check */
+
+ /* Make sure we can trim the buffer. */
+ optval[0] = 0;
+ ctx->optlen = 1;
+
+ /* Usepace buffer is PAGE_SIZE * 2, but BPF
+ * program can only see the first PAGE_SIZE
+ * bytes of data.
+ */
+ if (optval_end - optval != PAGE_SIZE)
+ return 0; /* EPERM, unexpected data size */
+
+ return 1;
+ }
if (ctx->level != SOL_CUSTOM)
return 0; /* EPERM, deny everything except custom level */