linux-hardening - [PATCH] misc: bcm-vk: Annotate struct bcm_vk_wkent with __counted

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Date: Fri, 22 Sep 2023 10:50:58 -0700
From: Kees Cook <keescook@...omium.org>
To: Scott Branden <scott.branden@...adcom.com>
Cc: Kees Cook <keescook@...omium.org>,
	Broadcom internal kernel review list <bcm-kernel-feedback-list@...adcom.com>,
	Arnd Bergmann <arnd@...db.de>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.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] misc: bcm-vk: Annotate struct bcm_vk_wkent 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 bcm_vk_wkent.
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: Scott Branden <scott.branden@...adcom.com>
Cc: Broadcom internal kernel review list <bcm-kernel-feedback-list@...adcom.com>
Cc: Arnd Bergmann <arnd@...db.de>
Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Signed-off-by: Kees Cook <keescook@...omium.org>
---
 drivers/misc/bcm-vk/bcm_vk_msg.c | 2 +-
 drivers/misc/bcm-vk/bcm_vk_msg.h | 2 +-
 2 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/misc/bcm-vk/bcm_vk_msg.c b/drivers/misc/bcm-vk/bcm_vk_msg.c
index e17d81231ea6..1f42d1d5a630 100644
--- a/drivers/misc/bcm-vk/bcm_vk_msg.c
+++ b/drivers/misc/bcm-vk/bcm_vk_msg.c
@@ -703,12 +703,12 @@ int bcm_vk_send_shutdown_msg(struct bcm_vk *vk, u32 shut_type,
 	entry = kzalloc(struct_size(entry, to_v_msg, 1), GFP_KERNEL);
 	if (!entry)
 		return -ENOMEM;
+	entry->to_v_blks = 1;	/* always 1 block */
 
 	/* fill up necessary data */
 	entry->to_v_msg[0].function_id = VK_FID_SHUTDOWN;
 	set_q_num(&entry->to_v_msg[0], q_num);
 	set_msg_id(&entry->to_v_msg[0], VK_SIMPLEX_MSG_ID);
-	entry->to_v_blks = 1; /* always 1 block */
 
 	entry->to_v_msg[0].cmd = shut_type;
 	entry->to_v_msg[0].arg = pid;
diff --git a/drivers/misc/bcm-vk/bcm_vk_msg.h b/drivers/misc/bcm-vk/bcm_vk_msg.h
index 56784c8896d8..157495e48f15 100644
--- a/drivers/misc/bcm-vk/bcm_vk_msg.h
+++ b/drivers/misc/bcm-vk/bcm_vk_msg.h
@@ -116,7 +116,7 @@ struct bcm_vk_wkent {
 	u32 usr_msg_id;
 	u32 to_v_blks;
 	u32 seq_num;
-	struct vk_msg_blk to_v_msg[];
+	struct vk_msg_blk to_v_msg[] __counted_by(to_v_blks);
 };
 
 /* queue stats counters */
-- 
2.34.1