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

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Date:   Fri, 15 Sep 2023 12:58:16 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Alan Stern <stern@...land.harvard.edu>
Cc:     Kees Cook <keescook@...omium.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Mathias Nyman <mathias.nyman@...el.com>,
        linux-usb@...r.kernel.org, Nathan Chancellor <nathan@...nel.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Tom Rix <trix@...hat.com>, linux-kernel@...r.kernel.org,
        llvm@...ts.linux.dev, linux-hardening@...r.kernel.org
Subject: [PATCH] usb: Annotate struct urb_priv 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 urb_priv.

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

Cc: Alan Stern <stern@...land.harvard.edu>
Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc: Mathias Nyman <mathias.nyman@...el.com>
Cc: linux-usb@...r.kernel.org
Signed-off-by: Kees Cook <keescook@...omium.org>
---
 drivers/usb/host/ohci.h | 2 +-
 drivers/usb/host/xhci.h | 2 +-
 2 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/usb/host/ohci.h b/drivers/usb/host/ohci.h
index aac6285b37f8..1aba22784e05 100644
--- a/drivers/usb/host/ohci.h
+++ b/drivers/usb/host/ohci.h
@@ -337,7 +337,7 @@ typedef struct urb_priv {
 	u16			length;		// # tds in this request
 	u16			td_cnt;		// tds already serviced
 	struct list_head	pending;
-	struct td		*td[];		// all TDs in this request
+	struct td		*td[] __counted_by(length); // all TDs in this request
 
 } urb_priv_t;
 
diff --git a/drivers/usb/host/xhci.h b/drivers/usb/host/xhci.h
index 7e282b4522c0..2f21c3a8565c 100644
--- a/drivers/usb/host/xhci.h
+++ b/drivers/usb/host/xhci.h
@@ -1666,7 +1666,7 @@ struct xhci_scratchpad {
 struct urb_priv {
 	int	num_tds;
 	int	num_tds_done;
-	struct	xhci_td	td[];
+	struct	xhci_td	td[] __counted_by(num_tds);
 };
 
 /*
-- 
2.34.1