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The ynl_attr_put_str() function was not including the null terminator in the attribute length calculation. This caused kernel to reject CTRL_CMD_GETFAMILY requests with EINVAL: "Attribute failed policy validation". For a 4-character family name like "dpll": - Sent: nla_len=8 (4 byte header + 4 byte string without null) - Expected: nla_len=9 (4 byte header + 5 byte string with null) The bug was introduced in commit15d2540e0d("tools: ynl: check for overflow of constructed messages") when refactoring from stpcpy() to strlen(). The original code correctly included the null terminator: end = stpcpy(ynl_attr_data(attr), str); attr->nla_len = NLA_HDRLEN + NLA_ALIGN(end - (char *)ynl_attr_data(attr)); Since stpcpy() returns a pointer past the null terminator, the length included it. The refactored version using strlen() omitted the +1. The fix also removes NLA_ALIGN() from nla_len calculation, since nla_len should contain actual attribute length, not aligned length. Alignment is only for calculating next attribute position. This makes the code consistent with ynl_attr_put(). CTRL_ATTR_FAMILY_NAME uses NLA_NUL_STRING policy which requires null terminator. Kernel validates with memchr() and rejects if not found. Fixes:15d2540e0d("tools: ynl: check for overflow of constructed messages") Signed-off-by: Petr Oros <poros@redhat.com> Tested-by: Ivan Vecera <ivecera@redhat.com> Reviewed-by: Ivan Vecera <ivecera@redhat.com> Link: https://lore.kernel.org/20251018151737.365485-3-zahari.doychev@linux.com Link: https://patch.msgid.link/20251024132438.351290-1-poros@redhat.com Signed-off-by: Jakub Kicinski <kuba@kernel.org>