linux-hardening - [PATCH] usb: gadget: f_midi: Annotate struct f_midi with __counted

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Date:   Fri, 15 Sep 2023 12:59:39 -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>,
        Peter Chen <peter.chen@....com>,
        Hulk Robot <hulkci@...wei.com>,
        Allen Pais <allen.lkml@...il.com>,
        Will McVicker <willmcvicker@...gle.com>,
        Davidlohr Bueso <dave@...olabs.net>,
        Zhang Qilong <zhangqilong3@...wei.com>,
        linux-usb@...r.kernel.org, Nathan Chancellor <nathan@...nel.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Tom Rix <trix@...hat.com>,
        Linyu Yuan <quic_linyyuan@...cinc.com>,
        linux-kernel@...r.kernel.org, llvm@...ts.linux.dev,
        linux-hardening@...r.kernel.org
Subject: [PATCH] usb: gadget: f_midi: Annotate struct f_midi 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 f_midi.
Additionally, since the element count member must be set before accessing
the annotated flexible array member, move its initialization earlier.

[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: Peter Chen <peter.chen@....com>
Cc: Hulk Robot <hulkci@...wei.com>
Cc: Allen Pais <allen.lkml@...il.com>
Cc: Will McVicker <willmcvicker@...gle.com>
Cc: Davidlohr Bueso <dave@...olabs.net>
Cc: Zhang Qilong <zhangqilong3@...wei.com>
Cc: linux-usb@...r.kernel.org
Signed-off-by: Kees Cook <keescook@...omium.org>
---
 drivers/usb/gadget/function/f_midi.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/usb/gadget/function/f_midi.c b/drivers/usb/gadget/function/f_midi.c
index 2d02f25f9597..033e347554db 100644
--- a/drivers/usb/gadget/function/f_midi.c
+++ b/drivers/usb/gadget/function/f_midi.c
@@ -99,7 +99,7 @@ struct f_midi {
 	unsigned int in_last_port;
 	unsigned char free_ref;
 
-	struct gmidi_in_port	in_ports_array[/* in_ports */];
+	struct gmidi_in_port	in_ports_array[] __counted_by(in_ports);
 };
 
 static inline struct f_midi *func_to_midi(struct usb_function *f)
@@ -1349,6 +1349,7 @@ static struct usb_function *f_midi_alloc(struct usb_function_instance *fi)
 		status = -ENOMEM;
 		goto setup_fail;
 	}
+	midi->in_ports = opts->in_ports;
 
 	for (i = 0; i < opts->in_ports; i++)
 		midi->in_ports_array[i].cable = i;
@@ -1359,7 +1360,6 @@ static struct usb_function *f_midi_alloc(struct usb_function_instance *fi)
 		status = -ENOMEM;
 		goto midi_free;
 	}
-	midi->in_ports = opts->in_ports;
 	midi->out_ports = opts->out_ports;
 	midi->index = opts->index;
 	midi->buflen = opts->buflen;
-- 
2.34.1