6.9-stable review patch. If anyone has any objections, please let me know.
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From: Nathan Chancellor nathan@kernel.org
commit 1c07c9be87dd3dd0634033bf08728b32465f08fb upstream.
Work for __counted_by on generic pointers in structures (not just flexible array members) has started landing in Clang 19 (current tip of tree). During the development of this feature, a restriction was added to __counted_by to prevent the flexible array member's element type from including a flexible array member itself such as:
struct foo { int count; char buf[]; };
struct bar { int count; struct foo data[] __counted_by(count); };
because the size of data cannot be calculated with the standard array size formula:
sizeof(struct foo) * count
This restriction was downgraded to a warning but due to CONFIG_WERROR, it can still break the build. The application of __counted_by on the ports member of 'struct mxser_board' triggers this restriction, resulting in:
drivers/tty/mxser.c:291:2: error: 'counted_by' should not be applied to an array with element of unknown size because 'struct mxser_port' is a struct type with a flexible array member. This will be an error in a future compiler version [-Werror,-Wbounds-safety-counted-by-elt-type-unknown-size] 291 | struct mxser_port ports[] __counted_by(nports); | ^~~~~~~~~~~~~~~~~~~~~~~~~ 1 error generated.
Remove this use of __counted_by to fix the warning/error. However, rather than remove it altogether, leave it commented, as it may be possible to support this in future compiler releases.
Cc: stable@vger.kernel.org Closes: https://github.com/ClangBuiltLinux/linux/issues/2026 Fixes: f34907ecca71 ("mxser: Annotate struct mxser_board with __counted_by") Signed-off-by: Nathan Chancellor nathan@kernel.org Link: https://lore.kernel.org/r/20240529-drop-counted-by-ports-mxser-board-v1-1-0a... Signed-off-by: Kees Cook kees@kernel.org Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- drivers/tty/mxser.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
--- a/drivers/tty/mxser.c +++ b/drivers/tty/mxser.c @@ -288,7 +288,7 @@ struct mxser_board { enum mxser_must_hwid must_hwid; speed_t max_baud;
- struct mxser_port ports[] __counted_by(nports); + struct mxser_port ports[] /* __counted_by(nports) */; };
static DECLARE_BITMAP(mxser_boards, MXSER_BOARDS);