libbpf: Correctly set the kernel code version in Debian kernel.

In a previous commit, Ubuntu kernel code version is correctly set
by retrieving the information from /proc/version_signature.

commit<5b3d72987701d51bf31823b39db49d10970f5c2d>
(libbpf: Improve LINUX_VERSION_CODE detection)

The /proc/version_signature file doesn't present in at least the
older versions of Debian distributions (eg, Debian 9, 10). The Debian
kernel has a similar issue where the release information from uname()
syscall doesn't give the kernel code version that matches what the
kernel actually expects. Below is an example content from Debian 10.

release: 4.19.0-23-amd64
version: kernel-patches#1 SMP Debian 4.19.269-1 (2022-12-20) x86_64

Debian reports incorrect kernel version in utsname::release returned
by uname() syscall, which in older kernels (Debian 9, 10) leads to
kprobe BPF programs failing to load due to the version check mismatch.

Fortunately, the correct kernel code version presents in the
utsname::version returned by uname() syscall in Debian kernels. This
change adds another get kernel version function to handle Debian in
addition to the previously added get kernel version function to handle
Ubuntu. Some minor refactoring work is also done to make the code more
readable.

Signed-off-by: Hao Xiang <[email protected]>
Signed-off-by: Ho-Ren (Jack) Chuang <[email protected]>
Signed-off-by: Andrii Nakryiko <[email protected]>
Link: https://lore.kernel.org/bpf/[email protected]

Author: haoxiangbd

tools/lib/bpf/libbpf.c

@@ -34,7 +34,6 @@
 #include <linux/limits.h>
 #include <linux/perf_event.h>
 #include <linux/ring_buffer.h>
-#include <linux/version.h>
 #include <sys/epoll.h>
 #include <sys/ioctl.h>
 #include <sys/mman.h>
@@ -870,42 +869,6 @@ bpf_object__add_programs(struct bpf_object *obj, Elf_Data *sec_data,
 	return 0;
 }
 
-__u32 get_kernel_version(void)
-{
-	/* On Ubuntu LINUX_VERSION_CODE doesn't correspond to info.release,
-	 * but Ubuntu provides /proc/version_signature file, as described at
-	 * https://ubuntu.com/kernel, with an example contents below, which we
-	 * can use to get a proper LINUX_VERSION_CODE.
-	 *
-	 *   Ubuntu 5.4.0-12.15-generic 5.4.8
-	 *
-	 * In the above, 5.4.8 is what kernel is actually expecting, while
-	 * uname() call will return 5.4.0 in info.release.
-	 */
-	const char *ubuntu_kver_file = "/proc/version_signature";
-	__u32 major, minor, patch;
-	struct utsname info;
-
-	if (faccessat(AT_FDCWD, ubuntu_kver_file, R_OK, AT_EACCESS) == 0) {
-		FILE *f;
-
-		f = fopen(ubuntu_kver_file, "r");
-		if (f) {
-			if (fscanf(f, "%*s %*s %d.%d.%d\n", &major, &minor, &patch) == 3) {
-				fclose(f);
-				return KERNEL_VERSION(major, minor, patch);
-			}
-			fclose(f);
-		}
-		/* something went wrong, fall back to uname() approach */
-	}
-
-	uname(&info);
-	if (sscanf(info.release, "%u.%u.%u", &major, &minor, &patch) != 3)
-		return 0;
-	return KERNEL_VERSION(major, minor, patch);
-}
-
 static const struct btf_member *
 find_member_by_offset(const struct btf_type *t, __u32 bit_offset)
 {

tools/lib/bpf/libbpf_probes.c

@@ -12,11 +12,94 @@
 #include <linux/btf.h>
 #include <linux/filter.h>
 #include <linux/kernel.h>
+#include <linux/version.h>
 
 #include "bpf.h"
 #include "libbpf.h"
 #include "libbpf_internal.h"
 
+/* On Ubuntu LINUX_VERSION_CODE doesn't correspond to info.release,
+ * but Ubuntu provides /proc/version_signature file, as described at
+ * https://ubuntu.com/kernel, with an example contents below, which we
+ * can use to get a proper LINUX_VERSION_CODE.
+ *
+ *   Ubuntu 5.4.0-12.15-generic 5.4.8
+ *
+ * In the above, 5.4.8 is what kernel is actually expecting, while
+ * uname() call will return 5.4.0 in info.release.
+ */
+static __u32 get_ubuntu_kernel_version(void)
+{
+	const char *ubuntu_kver_file = "/proc/version_signature";
+	__u32 major, minor, patch;
+	int ret;
+	FILE *f;
+
+	if (faccessat(AT_FDCWD, ubuntu_kver_file, R_OK, AT_EACCESS) != 0)
+		return 0;
+
+	f = fopen(ubuntu_kver_file, "r");
+	if (!f)
+		return 0;
+
+	ret = fscanf(f, "%*s %*s %u.%u.%u\n", &major, &minor, &patch);
+	fclose(f);
+	if (ret != 3)
+		return 0;
+
+	return KERNEL_VERSION(major, minor, patch);
+}
+
+/* On Debian LINUX_VERSION_CODE doesn't correspond to info.release.
+ * Instead, it is provided in info.version. An example content of
+ * Debian 10 looks like the below.
+ *
+ *   utsname::release   4.19.0-22-amd64
+ *   utsname::version   #1 SMP Debian 4.19.260-1 (2022-09-29)
+ *
+ * In the above, 4.19.260 is what kernel is actually expecting, while
+ * uname() call will return 4.19.0 in info.release.
+ */
+static __u32 get_debian_kernel_version(struct utsname *info)
+{
+	__u32 major, minor, patch;
+	char *p;
+
+	p = strstr(info->version, "Debian ");
+	if (!p) {
+		/* This is not a Debian kernel. */
+		return 0;
+	}
+
+	if (sscanf(p, "Debian %u.%u.%u", &major, &minor, &patch) != 3)
+		return 0;
+
+	return KERNEL_VERSION(major, minor, patch);
+}
+
+__u32 get_kernel_version(void)
+{
+	__u32 major, minor, patch, version;
+	struct utsname info;
+
+	/* Check if this is an Ubuntu kernel. */
+	version = get_ubuntu_kernel_version();
+	if (version != 0)
+		return version;
+
+	uname(&info);
+
+	/* Check if this is a Debian kernel. */
+	version = get_debian_kernel_version(&info);
+	if (version != 0)
+		return version;
+
+	if (sscanf(info.release, "%u.%u.%u", &major, &minor, &patch) != 3)
+		return 0;
+
+	return KERNEL_VERSION(major, minor, patch);
+}
+
 static int probe_prog_load(enum bpf_prog_type prog_type,
 			   const struct bpf_insn *insns, size_t insns_cnt,
 			   char *log_buf, size_t log_buf_sz)