linux-kernel - [PATCH] usb: gadget: f_fs: Annotate struct ffs_buffer with __counted

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Date:   Fri, 15 Sep 2023 12:58:49 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     Kees Cook <keescook@...omium.org>,
        John Keeping <john@...ping.me.uk>,
        Udipto Goswami <quic_ugoswami@...cinc.com>,
        Linyu Yuan <quic_linyyuan@...cinc.com>,
        linux-usb@...r.kernel.org, Nathan Chancellor <nathan@...nel.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Tom Rix <trix@...hat.com>,
        Krishna Kurapati <quic_kriskura@...cinc.com>,
        Jeff Layton <jlayton@...nel.org>,
        Uttkarsh Aggarwal <quic_uaggarwa@...cinc.com>,
        Yuta Hayama <hayama@...eo.co.jp>, linux-kernel@...r.kernel.org,
        llvm@...ts.linux.dev, linux-hardening@...r.kernel.org
Subject: [PATCH] usb: gadget: f_fs: Annotate struct ffs_buffer with __counted_by

Prepare for the coming implementation by GCC and Clang of the __counted_by
attribute. Flexible array members annotated with __counted_by can have
their accesses bounds-checked at run-time checking via CONFIG_UBSAN_BOUNDS
(for array indexing) and CONFIG_FORTIFY_SOURCE (for strcpy/memcpy-family
functions).

As found with Coccinelle[1], add __counted_by for struct ffs_buffer.

[1] https://github.com/kees/kernel-tools/blob/trunk/coccinelle/examples/counted_by.cocci

Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc: John Keeping <john@...ping.me.uk>
Cc: Udipto Goswami <quic_ugoswami@...cinc.com>
Cc: Linyu Yuan <quic_linyyuan@...cinc.com>
Cc: linux-usb@...r.kernel.org
Signed-off-by: Kees Cook <keescook@...omium.org>
---
 drivers/usb/gadget/function/f_fs.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/usb/gadget/function/f_fs.c b/drivers/usb/gadget/function/f_fs.c
index 6e9ef35a43a7..af400d083777 100644
--- a/drivers/usb/gadget/function/f_fs.c
+++ b/drivers/usb/gadget/function/f_fs.c
@@ -202,7 +202,7 @@ struct ffs_epfile {
 struct ffs_buffer {
 	size_t length;
 	char *data;
-	char storage[];
+	char storage[] __counted_by(length);
 };
 
 /*  ffs_io_data structure ***************************************************/
-- 
2.34.1