The log buffer of common attributes would be confusing with the one in
'union bpf_attr' for BPF_PROG_LOAD.

In order to clarify the usage of these two log buffers, they both can be
used for logging if:

* They are same, including 'log_buf', 'log_level' and 'log_size'.
* One of them is missing, then another one will be used for logging.

If they both have 'log_buf' but they are not same totally, return -EUSERS.

Signed-off-by: Leon Hwang <leon.hwang@linux.dev>
---
 kernel/bpf/syscall.c | 55 ++++++++++++++++++++++++++++++++++++++++++--
 1 file changed, 53 insertions(+), 2 deletions(-)

diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
index 2bdc0b43ec832..698c30ff99486 100644
--- a/kernel/bpf/syscall.c
+++ b/kernel/bpf/syscall.c
@@ -6092,11 +6092,57 @@ static int prog_stream_read(union bpf_attr *attr)
 	return ret;
 }
 
-static int copy_prog_load_log_true_size(union bpf_attr *attr, bpfptr_t uattr, unsigned int size)
+static int check_log_attrs(u64 log_buf, u32 log_size, u32 log_level,
+			   struct bpf_common_attr *common_attrs)
+{
+	if (log_buf && common_attrs->log_buf && (log_buf != common_attrs->log_buf ||
+						 log_size != common_attrs->log_size ||
+						 log_level != common_attrs->log_level))
+		return -EUSERS;
+
+	return 0;
+}
+
+static int check_prog_load_log_attrs(union bpf_attr *attr, struct bpf_common_attr *common_attrs,
+				     bool *log_common_attrs)
+{
+	int err;
+
+	err = check_log_attrs(attr->log_buf, attr->log_size, attr->log_level, common_attrs);
+	if (err)
+		return err;
+
+	if (!attr->log_buf && common_attrs->log_buf) {
+		*log_common_attrs = true;
+		attr->log_buf = common_attrs->log_buf;
+		attr->log_size = common_attrs->log_size;
+		attr->log_level = common_attrs->log_level;
+	}
+
+	return 0;
+}
+
+static int __copy_common_attr_log_true_size(bpfptr_t uattr, unsigned int size, u32 *log_true_size)
+{
+	if (size >= offsetofend(struct bpf_common_attr, log_true_size) &&
+	    copy_to_bpfptr_offset(uattr, offsetof(struct bpf_common_attr, log_true_size),
+				  log_true_size, sizeof(*log_true_size)))
+		return -EFAULT;
+
+	return 0;
+}
+
+static int copy_prog_load_log_true_size(union bpf_attr *attr, bpfptr_t uattr, unsigned int size,
+					struct bpf_common_attr *common_attrs, bpfptr_t uattr_common,
+					unsigned int size_common, bool log_common_attrs)
 {
 	if (!attr->log_true_size)
 		return 0;
 
+	if (log_common_attrs)
+		return __copy_common_attr_log_true_size(uattr_common, size_common,
+							&attr->log_true_size);
+
 	if (size >= offsetofend(union bpf_attr, log_true_size) &&
 	    copy_to_bpfptr_offset(uattr, offsetof(union bpf_attr, log_true_size),
 				  &attr->log_true_size, sizeof(attr->log_true_size)))
@@ -6109,6 +6155,7 @@ static int __sys_bpf(enum bpf_cmd cmd, bpfptr_t uattr, unsigned int size,
 		     bpfptr_t uattr_common, unsigned int size_common)
 {
 	struct bpf_common_attr common_attrs;
+	bool log_common_attrs = false;
 	union bpf_attr attr;
 	int err, ret;
 
@@ -6158,9 +6205,13 @@ static int __sys_bpf(enum bpf_cmd cmd, bpfptr_t uattr, unsigned int size,
 		err = map_freeze(&attr);
 		break;
 	case BPF_PROG_LOAD:
+		err = check_prog_load_log_attrs(&attr, &common_attrs, &log_common_attrs);
+		if (err)
+			break;
 		attr.log_true_size = 0;
 		err = bpf_prog_load(&attr, uattr);
-		ret = copy_prog_load_log_true_size(&attr, uattr, size);
+		ret = copy_prog_load_log_true_size(&attr, uattr, size, &common_attrs, uattr_common,
+						   size_common, log_common_attrs);
 		err = ret ? ret : err;
 		break;
 	case BPF_OBJ_PIN:
-- 
2.51.0