UAPI: ethtool: Avoid flex-array in struct ethtool_link_settings

struct ethtool_link_settings tends to be used as a header for other
structures that have trailing bytes[1], but has a trailing flexible array
itself. Using this overlapped with other structures leads to ambiguous
object sizing in the compiler, so we want to avoid such situations (which
have caused real bugs in the past). Detecting this can be done with
-Wflex-array-member-not-at-end, which will need to be enabled globally.

Using a tagged struct_group() to create a new ethtool_link_settings_hdr
structure isn't possible as it seems we cannot use the tagged variant of
struct_group() due to syntax issues from C++'s perspective (even within
"extern C")[2]. Instead, we can just leave the offending member defined
in UAPI and remove it from the kernel's view of the structure, as Linux
doesn't actually use this member at all. There is also no change in
size since it was already a flexible array that didn't contribute to
size returned by any use of sizeof().

Reported-by: Jakub Kicinski <kuba@kernel.org>
Closes: https://lore.kernel.org/lkml/20241109100213.262a2fa0@kernel.org/ [2]
Link: https://lore.kernel.org/lkml/0bc2809fe2a6c11dd4c8a9a10d9bd65cccdb559b.1730238285.git.gustavoars@kernel.org/ [1]
Signed-off-by: Kees Cook <kees@kernel.org>
Reviewed-by: Jakub Kicinski <kuba@kernel.org>
Link: https://patch.msgid.link/20241115204308.3821419-3-kees@kernel.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

0 files changed, 0 insertions, 0 deletions