linux-kernel - [PATCH 2/5] watch_queue: Make watch_sizeof() check record size [ver #2]

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Date:   Mon, 03 Aug 2020 14:06:37 +0100
From:   David Howells <dhowells@...hat.com>
To:     viro@...iv.linux.org.uk
Cc:     Miklos Szeredi <mszeredi@...hat.com>, dhowells@...hat.com,
        torvalds@...ux-foundation.org, casey@...aufler-ca.com,
        sds@...ho.nsa.gov, nicolas.dichtel@...nd.com, raven@...maw.net,
        christian@...uner.io, jlayton@...hat.com, kzak@...hat.com,
        mszeredi@...hat.com, linux-api@...r.kernel.org,
        linux-fsdevel@...r.kernel.org,
        linux-security-module@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [PATCH 2/5] watch_queue: Make watch_sizeof() check record size [ver
 #2]

Make watch_sizeof() give a build error if the size of the struct won't fit
into the size field in the header.

Reported-by: Miklos Szeredi <mszeredi@...hat.com>
Signed-off-by: David Howells <dhowells@...hat.com>
---

 include/linux/watch_queue.h |    7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/include/linux/watch_queue.h b/include/linux/watch_queue.h
index 5e08db2adc31..38e04c7a7951 100644
--- a/include/linux/watch_queue.h
+++ b/include/linux/watch_queue.h
@@ -120,7 +120,12 @@ static inline void remove_watch_list(struct watch_list *wlist, u64 id)
  * watch_sizeof - Calculate the information part of the size of a watch record,
  * given the structure size.
  */
-#define watch_sizeof(STRUCT) (sizeof(STRUCT) << WATCH_INFO_LENGTH__SHIFT)
+#define watch_sizeof(STRUCT) \
+	({								\
+		size_t max = WATCH_INFO_LENGTH >> WATCH_INFO_LENGTH__SHIFT; \
+		BUILD_BUG_ON(sizeof(STRUCT) > max);			\
+		sizeof(STRUCT) << WATCH_INFO_LENGTH__SHIFT;		\
+	})
 
 #endif