Fix kprobe_multi interface issues for 5.18

Check that size would not overflow before calculation (and return -EOVERFLOW if it will), to prevent potential out-of-bounds write with the following copy_from_user. Add the same check
to kprobe_multi_resolve_syms in case it will be called from elsewhere in the future. The INT_MAX checks are performed in order to avoid triggering kvmalloc_node warning [1].

[1] https://lore.kernel.org/lkml/[email protected]/

Fixes 0dcac272540613d4 ("bpf: Add multi kprobe link")

Signed-off-by Eugene Syromiatnikov <[email protected]>

With the interface as defined, it is impossible to pass 64-bit kernel addresses from a 32-bit userspace process in BPF_LINK_TYPE_KPROBE_MULTI, which severly limits the useability of the interface, change the API to accept an array of u64 values instead of (kernel? user?) longs. This patch implements the user space part of the change (without the relevant kernel changes, since, as of now, an attempt to add kprobe_multi link will fail with -EOPNOTSUPP), to avoid changing the interface after a release.

Fixes 5117c26e877352bc ("libbpf: Add bpf_link_create support for multi kprobes")

Fixes ddc6b04989eb0993 ("libbpf: Add bpf_program__attach_kprobe_multi_opts function")

Fixes f7a11eeccb111854 ("selftests/bpf: Add kprobe_multi attach test")

Fixes 9271a0c7ae7a9147 ("selftests/bpf: Add attach test for bpf_program__attach_kprobe_multi_opts")

Fixes 2c6401c966ae1fbe ("selftests/bpf: Add kprobe_multi bpf_cookie test")

Signed-off-by Eugene Syromiatnikov <[email protected]>

---
  tools/lib/bpf/bpf.h                                        | 2 +-
  tools/lib/bpf/libbpf.c                                     | 8 ++++----
  tools/lib/bpf/libbpf.h                                     | 2 +-
  tools/testing/selftests/bpf/prog_tests/bpf_cookie.c        | 2 +-
  tools/testing/selftests/bpf/prog_tests/kprobe_multi_test.c | 8 ++++----
  5 files changed, 11 insertions(+), 11 deletions(-)

tools/lib/bpf/bpf.h +0 -0

index f4b4afb..f677602 100644

tools/lib/bpf/bpf.h +0 -0

  			const __u64 *cookies;
  		} kprobe_multi;
  	};

tools/lib/bpf/libbpf.c +4 -4

index 809fe20..03a14a6 100644
@@ -10279,7 +10279,7 @@ static bool glob_match(const char *str, const char *pat)
 
  struct kprobe_multi_resolve {
  	const char *pattern;
-	unsigned long *addrs;
+	__u64 *addrs;
  	size_t cap;
  	size_t cnt;
  };

@@ -10294,12 +10294,12 @@ resolve_kprobe_multi_cb(unsigned long long sym_addr, char sym_type,
  	if (!glob_match(sym_name, res->pattern))
  		return 0;
 
-	err = libbpf_ensure_mem((void **) &res->addrs, &res->cap, sizeof(unsigned long),
+	err = libbpf_ensure_mem((void **) &res->addrs, &res->cap, sizeof(__u64),
  				res->cnt + 1);
  	if (err)
  		return err;
 
-	res->addrs[res->cnt++] = (unsigned long) sym_addr;
+	res->addrs[res->cnt++] = sym_addr;
  	return 0;
  }
 

@@ -10314,7 +10314,7 @@ bpf_program__attach_kprobe_multi_opts(const struct bpf_program *prog,
  	};
  	struct bpf_link *link = NULL;
  	char errmsg[STRERR_BUFSIZE];
-	const unsigned long *addrs;
+	const __u64 *addrs;
  	int err, link_fd, prog_fd;
  	const __u64 *cookies;
  	const char **syms;

tools/lib/bpf/libbpf.h +1 -1

index 05dde85..ec1cb61 100644
@@ -431,7 +431,7 @@ struct bpf_kprobe_multi_opts {
  	/* array of function symbols to attach */
  	const char **syms;
  	/* array of function addresses to attach */
-	const unsigned long *addrs;
+	const __u64 *addrs;
  	/* array of user-provided values fetchable through bpf_get_attach_cookie */
  	const __u64 *cookies;
  	/* number of elements in syms/addrs/cookies arrays */

tools/testing/selftests/bpf/prog_tests/bpf_cookie.c +1 -1

index 923a613..5aa482a 100644
@@ -137,7 +137,7 @@ static void kprobe_multi_link_api_subtest(void)
  	cookies[6] = 7;
  	cookies[7] = 8;
 
-	opts.kprobe_multi.addrs = (const unsigned long *) &addrs;
+	opts.kprobe_multi.addrs = (const __u64 *) &addrs;
  	opts.kprobe_multi.cnt = ARRAY_SIZE(addrs);
  	opts.kprobe_multi.cookies = (const __u64 *) &cookies;
  	prog_fd = bpf_program__fd(skel->progs.test_kprobe);

tools/testing/selftests/bpf/prog_tests/kprobe_multi_test.c +4 -4

index b9876b5..fbf4cf2 100644
@@ -105,7 +105,7 @@ static void test_link_api_addrs(void)
  	GET_ADDR("bpf_fentry_test7", addrs[6]);
  	GET_ADDR("bpf_fentry_test8", addrs[7]);
 
-	opts.kprobe_multi.addrs = (const unsigned long*) addrs;
+	opts.kprobe_multi.addrs = (const __u64 *) addrs;
  	opts.kprobe_multi.cnt = ARRAY_SIZE(addrs);
  	test_link_api(&opts);
  }

@@ -183,7 +183,7 @@ static void test_attach_api_addrs(void)
  	GET_ADDR("bpf_fentry_test7", addrs[6]);
  	GET_ADDR("bpf_fentry_test8", addrs[7]);
 
-	opts.addrs = (const unsigned long *) addrs;
+	opts.addrs = (const __u64 *) addrs;
  	opts.cnt = ARRAY_SIZE(addrs);
  	test_attach_api(NULL, &opts);
  }

@@ -241,7 +241,7 @@ static void test_attach_api_fails(void)
  		goto cleanup;
 
  	/* fail_2 - both addrs and syms set */
-	opts.addrs = (const unsigned long *) addrs;
+	opts.addrs = (const __u64 *) addrs;
  	opts.syms = syms;
  	opts.cnt = ARRAY_SIZE(syms);
  	opts.cookies = NULL;

@@ -255,7 +255,7 @@ static void test_attach_api_fails(void)
  		goto cleanup;
 
  	/* fail_3 - pattern and addrs set */
-	opts.addrs = (const unsigned long *) addrs;
+	opts.addrs = (const __u64 *) addrs;
  	opts.syms = NULL;
  	opts.cnt = ARRAY_SIZE(syms);
  	opts.cookies = NULL;

Quoted 32 lines · Eugene Syromiatnikov

With the interface as defined, it is impossible to pass 64-bit kernel addresses from a 32-bit userspace process in BPF_LINK_TYPE_KPROBE_MULTI, which severly limits the useability of the interface, change the API to accept an array of u64 values instead of (kernel? user?) longs. This patch implements the user space part of the change (without the relevant kernel changes, since, as of now, an attempt to add kprobe_multi link will fail with -EOPNOTSUPP), to avoid changing the interface after a release.

Fixes 5117c26e877352bc ("libbpf: Add bpf_link_create support for multi kprobes")

Fixes ddc6b04989eb0993 ("libbpf: Add bpf_program__attach_kprobe_multi_opts function")

Fixes f7a11eeccb111854 ("selftests/bpf: Add kprobe_multi attach test")

Fixes 9271a0c7ae7a9147 ("selftests/bpf: Add attach test for bpf_program__attach_kprobe_multi_opts")

Fixes 2c6401c966ae1fbe ("selftests/bpf: Add kprobe_multi bpf_cookie test")

Signed-off-by Eugene Syromiatnikov <[email protected]>

---
  tools/lib/bpf/bpf.h                                        | 2 +-
  tools/lib/bpf/libbpf.c                                     | 8 ++++----
  tools/lib/bpf/libbpf.h                                     | 2 +-
  tools/testing/selftests/bpf/prog_tests/bpf_cookie.c        | 2 +-
  tools/testing/selftests/bpf/prog_tests/kprobe_multi_test.c | 8 ++++----
  5 files changed, 11 insertions(+), 11 deletions(-)

tools/lib/bpf/bpf.h +0 -1

index f4b4afb..f677602 100644
@@ -417,7 +417,7 @@ struct bpf_link_create_opts {
  			__u32 flags;
  			__u32 cnt;
  			const char **syms;
-			const unsigned long *addrs;

tools/lib/bpf/bpf.h struct bpf_link_create_opts { · line 420

Quoted 1 line

tools/lib/bpf/bpf.h +1 -0

+			const __u64 *addrs;

Patch 2 and 3 will prevent supporting 64-bit kernel, 32-bit userspace for kprobe_multi. So effectively, kprobe_multi only supports 64-bit kernel and 64-bit user space.
This is definitely an option, but it would be great
if other people can chime in as well for whether this choice is best or not.

Quoted 98 lines

tools/lib/bpf/bpf.h +0 -0

  			const __u64 *cookies;
  		} kprobe_multi;
  	};

tools/lib/bpf/libbpf.c +4 -4

index 809fe20..03a14a6 100644
@@ -10279,7 +10279,7 @@ static bool glob_match(const char *str, const char *pat)
  struct kprobe_multi_resolve {
  	const char *pattern;
-	unsigned long *addrs;
+	__u64 *addrs;
  	size_t cap;
  	size_t cnt;
  };

@@ -10294,12 +10294,12 @@ resolve_kprobe_multi_cb(unsigned long long sym_addr, char sym_type,
  	if (!glob_match(sym_name, res->pattern))
  		return 0;
-	err = libbpf_ensure_mem((void **) &res->addrs, &res->cap, sizeof(unsigned long),
+	err = libbpf_ensure_mem((void **) &res->addrs, &res->cap, sizeof(__u64),
  				res->cnt + 1);
  	if (err)
  		return err;
-	res->addrs[res->cnt++] = (unsigned long) sym_addr;
+	res->addrs[res->cnt++] = sym_addr;
  	return 0;
  }

@@ -10314,7 +10314,7 @@ bpf_program__attach_kprobe_multi_opts(const struct bpf_program *prog,
  	};
  	struct bpf_link *link = NULL;
  	char errmsg[STRERR_BUFSIZE];
-	const unsigned long *addrs;
+	const __u64 *addrs;
  	int err, link_fd, prog_fd;
  	const __u64 *cookies;
  	const char **syms;

tools/lib/bpf/libbpf.h +1 -1

index 05dde85..ec1cb61 100644
@@ -431,7 +431,7 @@ struct bpf_kprobe_multi_opts {
  	/* array of function symbols to attach */
  	const char **syms;
  	/* array of function addresses to attach */
-	const unsigned long *addrs;
+	const __u64 *addrs;
  	/* array of user-provided values fetchable through bpf_get_attach_cookie */
  	const __u64 *cookies;
  	/* number of elements in syms/addrs/cookies arrays */

tools/testing/selftests/bpf/prog_tests/bpf_cookie.c +1 -1

index 923a613..5aa482a 100644
@@ -137,7 +137,7 @@ static void kprobe_multi_link_api_subtest(void)
  	cookies[6] = 7;
  	cookies[7] = 8;
-	opts.kprobe_multi.addrs = (const unsigned long *) &addrs;
+	opts.kprobe_multi.addrs = (const __u64 *) &addrs;
  	opts.kprobe_multi.cnt = ARRAY_SIZE(addrs);
  	opts.kprobe_multi.cookies = (const __u64 *) &cookies;
  	prog_fd = bpf_program__fd(skel->progs.test_kprobe);

tools/testing/selftests/bpf/prog_tests/kprobe_multi_test.c +4 -4

index b9876b5..fbf4cf2 100644
@@ -105,7 +105,7 @@ static void test_link_api_addrs(void)
  	GET_ADDR("bpf_fentry_test7", addrs[6]);
  	GET_ADDR("bpf_fentry_test8", addrs[7]);
-	opts.kprobe_multi.addrs = (const unsigned long*) addrs;
+	opts.kprobe_multi.addrs = (const __u64 *) addrs;
  	opts.kprobe_multi.cnt = ARRAY_SIZE(addrs);
  	test_link_api(&opts);
  }

@@ -183,7 +183,7 @@ static void test_attach_api_addrs(void)
  	GET_ADDR("bpf_fentry_test7", addrs[6]);
  	GET_ADDR("bpf_fentry_test8", addrs[7]);
-	opts.addrs = (const unsigned long *) addrs;
+	opts.addrs = (const __u64 *) addrs;
  	opts.cnt = ARRAY_SIZE(addrs);
  	test_attach_api(NULL, &opts);
  }

@@ -241,7 +241,7 @@ static void test_attach_api_fails(void)
  		goto cleanup;
  	/* fail_2 - both addrs and syms set */
-	opts.addrs = (const unsigned long *) addrs;
+	opts.addrs = (const __u64 *) addrs;
  	opts.syms = syms;
  	opts.cnt = ARRAY_SIZE(syms);
  	opts.cookies = NULL;

@@ -255,7 +255,7 @@ static void test_attach_api_fails(void)
  		goto cleanup;
  	/* fail_3 - pattern and addrs set */
-	opts.addrs = (const unsigned long *) addrs;
+	opts.addrs = (const __u64 *) addrs;
  	opts.syms = NULL;
  	opts.cnt = ARRAY_SIZE(syms);
  	opts.cookies = NULL;

Hello.

While [1] seems to require additional work[2] due to changes in the interface (and it has already been re-targeted for bpf-next), I would like to ask to consider the following three patches, that fix possible out-of-bounds write, properly disable the interface for 32-bit compat user space, and prepare the libbpf interface change, for the 5.18 release. Thank you.