linux-kernel - [PATCH 1/2] iov_iter: mark truncated iters

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Message-Id: <a2c762e46ede42470f4dd9aafb927466bd363943.1628509745.git.asml.silence@gmail.com>
Date:   Mon,  9 Aug 2021 12:52:36 +0100
From:   Pavel Begunkov <asml.silence@...il.com>
To:     Alexander Viro <viro@...iv.linux.org.uk>,
        linux-fsdevel@...r.kernel.org, Jens Axboe <axboe@...nel.dk>,
        io-uring@...r.kernel.org
Cc:     linux-kernel@...r.kernel.org, asml.silence@...il.com
Subject: [PATCH 1/2] iov_iter: mark truncated iters

Track if an iterator has ever been truncated. This will be used to
mitigate revert-truncate problems.

Signed-off-by: Pavel Begunkov <asml.silence@...il.com>
---
 include/linux/uio.h | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/include/linux/uio.h b/include/linux/uio.h
index 82c3c3e819e0..61b8d312d13a 100644
--- a/include/linux/uio.h
+++ b/include/linux/uio.h
@@ -30,6 +30,7 @@ enum iter_type {
 struct iov_iter {
 	u8 iter_type;
 	bool data_source;
+	bool truncated;
 	size_t iov_offset;
 	size_t count;
 	union {
@@ -254,8 +255,10 @@ static inline void iov_iter_truncate(struct iov_iter *i, u64 count)
 	 * conversion in assignement is by definition greater than all
 	 * values of size_t, including old i->count.
 	 */
-	if (i->count > count)
+	if (i->count > count) {
 		i->count = count;
+		i->truncated = true;
+	}
 }
 
 /*
-- 
2.32.0