fix: zero the genlmsghdr reserved field in Genlmsg

aarcamp · aboch · commit 9c2aece9c613 · 2026-06-10T10:57:38.000-07:00
The kernel struct is defined as follows:

	struct genlmsghdr {
                __u8    cmd;
                __u8    version;
                __u16   reserved;
        };

Genlmsg declared only Command and Version (2 bytes), but SizeofGenlmsg
is 4 and Serialize() unsafe-casts the struct to [4]byte. The extra two
bytes contained arbitrary contents read from adjacent memory and emitted
as the genlmsghdr reserved field.

The kernel's genl_header_check() conditionally rejects a non-zero
reserved field with EINVAL ("genlmsghdr.reserved field is not 0") which
surfaced when adding new netdev commands.

Add an explicit Reserved uint16 field so the struct is genuinely 4 bytes
and serializes the reserved word as zero.

Signed-off-by: Aaron Campbell &lt;aaron@monkey.org&gt;
diff --git a/nl/genetlink_linux.go b/nl/genetlink_linux.go
@@ -72,8 +72,9 @@ const (
 )
 
 type Genlmsg struct {
-	Command uint8
-	Version uint8
+	Command  uint8
+	Version  uint8
+	Reserved uint16
 }
 
 func (msg *Genlmsg) Len() int {

Original file line number	Diff line number	Diff line change
`@@ -72,8 +72,9 @@ const (`
`72`	`72`	`)`
`73`	`73`
`74`	`74`	`type Genlmsg struct {`
`75`		`- Command uint8`
`76`		`- Version uint8`
	`75`	`+ Command uint8`
	`76`	`+ Version uint8`
	`77`	`+ Reserved uint16`
`77`	`78`	`}`
`78`	`79`
`79`	`80`	`func (msg *Genlmsg) Len() int {`