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Message-Id: <20200617010416.93086-2-sdf@google.com>
Date: Tue, 16 Jun 2020 18:04:15 -0700
From: Stanislav Fomichev <sdf@...gle.com>
To: netdev@...r.kernel.org, bpf@...r.kernel.org
Cc: davem@...emloft.net, ast@...nel.org, daniel@...earbox.net,
Stanislav Fomichev <sdf@...gle.com>
Subject: [PATCH bpf v5 2/3] selftests/bpf: make sure optvals > PAGE_SIZE are bypassed
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@...gle.com>
---
.../selftests/bpf/prog_tests/sockopt_sk.c | 46 +++++++++++++---
.../testing/selftests/bpf/progs/sockopt_sk.c | 54 ++++++++++++++++++-
2 files changed, 91 insertions(+), 9 deletions(-)
diff --git a/tools/testing/selftests/bpf/prog_tests/sockopt_sk.c b/tools/testing/selftests/bpf/prog_tests/sockopt_sk.c
index 2061a6beac0f..5f54c6aec7f0 100644
--- a/tools/testing/selftests/bpf/prog_tests/sockopt_sk.c
+++ b/tools/testing/selftests/bpf/prog_tests/sockopt_sk.c
@@ -13,6 +13,7 @@ static int getsetsockopt(void)
char cc[16]; /* TCP_CA_NAME_MAX */
} buf = {};
socklen_t optlen;
+ char *big_buf = NULL;
fd = socket(AF_INET, SOCK_STREAM, 0);
if (fd < 0) {
@@ -22,24 +23,31 @@ static int getsetsockopt(void)
/* IP_TOS - BPF bypass */
- buf.u8[0] = 0x08;
- err = setsockopt(fd, SOL_IP, IP_TOS, &buf, 1);
+ optlen = getpagesize() * 2;
+ big_buf = calloc(1, optlen);
+ if (!big_buf) {
+ log_err("Couldn't allocate two pages");
+ goto err;
+ }
+
+ *(int *)big_buf = 0x08;
+ err = setsockopt(fd, SOL_IP, IP_TOS, big_buf, optlen);
if (err) {
log_err("Failed to call setsockopt(IP_TOS)");
goto err;
}
- buf.u8[0] = 0x00;
+ memset(big_buf, 0, optlen);
optlen = 1;
- err = getsockopt(fd, SOL_IP, IP_TOS, &buf, &optlen);
+ err = getsockopt(fd, SOL_IP, IP_TOS, big_buf, &optlen);
if (err) {
log_err("Failed to call getsockopt(IP_TOS)");
goto err;
}
- if (buf.u8[0] != 0x08) {
- log_err("Unexpected getsockopt(IP_TOS) buf[0] 0x%02x != 0x08",
- buf.u8[0]);
+ if (*(int *)big_buf != 0x08) {
+ log_err("Unexpected getsockopt(IP_TOS) optval 0x%x != 0x08",
+ *(int *)big_buf);
goto err;
}
@@ -78,6 +86,28 @@ static int getsetsockopt(void)
goto err;
}
+ /* IP_FREEBIND - BPF can't access optval past PAGE_SIZE */
+
+ optlen = getpagesize() * 2;
+ memset(big_buf, 0, optlen);
+
+ err = setsockopt(fd, SOL_IP, IP_FREEBIND, big_buf, optlen);
+ if (err != 0) {
+ log_err("Failed to call setsockopt, ret=%d", err);
+ goto err;
+ }
+
+ err = getsockopt(fd, SOL_IP, IP_FREEBIND, big_buf, &optlen);
+ if (err != 0) {
+ log_err("Failed to call getsockopt, ret=%d", err);
+ goto err;
+ }
+
+ if (optlen != 1 || *(__u8 *)big_buf != 0x55) {
+ log_err("Unexpected IP_FREEBIND getsockopt, optlen=%d, optval=0x%x",
+ optlen, *(__u8 *)big_buf);
+ }
+
/* SO_SNDBUF is overwritten */
buf.u32 = 0x01010101;
@@ -124,9 +154,11 @@ static int getsetsockopt(void)
goto err;
}
+ free(big_buf);
close(fd);
return 0;
err:
+ free(big_buf);
close(fd);
return -1;
}
diff --git a/tools/testing/selftests/bpf/progs/sockopt_sk.c b/tools/testing/selftests/bpf/progs/sockopt_sk.c
index d5a5eeb5fb52..712df7b49cb1 100644
--- a/tools/testing/selftests/bpf/progs/sockopt_sk.c
+++ b/tools/testing/selftests/bpf/progs/sockopt_sk.c
@@ -8,6 +8,10 @@
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 {
@@ -28,12 +32,14 @@ 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;
@@ -51,6 +57,26 @@ 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 */
@@ -81,12 +107,14 @@ 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 */
@@ -112,6 +140,28 @@ 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 */
--
2.27.0.290.gba653c62da-goog
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