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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@google.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/20200617010416.93086-2-sdf@google.com
This commit is contained in:
Stanislav Fomichev 2020-06-16 18:04:15 -07:00 committed by Alexei Starovoitov
parent d8fe449a9c
commit a0cb12b031
2 changed files with 91 additions and 9 deletions
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46
tools/testing/selftests/bpf/prog_tests/sockopt_sk.c
View File

@ -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;
}

54
tools/testing/selftests/bpf/progs/sockopt_sk.c
View File

@ -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 */