linux-kernel - [PATCH AUTOSEL 4.4 7/9] PM: hibernate: Fix snapshot partial write lengths

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Message-Id: <20211130145402.947049-7-sashal@kernel.org>
Date:   Tue, 30 Nov 2021 09:54:00 -0500
From:   Sasha Levin <sashal@...nel.org>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
Cc:     Evan Green <evgreen@...omium.org>,
        "Rafael J . Wysocki" <rafael.j.wysocki@...el.com>,
        Sasha Levin <sashal@...nel.org>, rafael@...nel.org,
        pavel@....cz, len.brown@...el.com, linux-pm@...r.kernel.org
Subject: [PATCH AUTOSEL 4.4 7/9] PM: hibernate: Fix snapshot partial write lengths

From: Evan Green <evgreen@...omium.org>

[ Upstream commit 88a5045f176b78c33a269a30a7b146e99c550bd9 ]

snapshot_write() is inappropriately limiting the amount of data that can
be written in cases where a partial page has already been written. For
example, one would expect to be able to write 1 byte, then 4095 bytes to
the snapshot device, and have both of those complete fully (since now
we're aligned to a page again). But what ends up happening is we write 1
byte, then 4094/4095 bytes complete successfully.

The reason is that simple_write_to_buffer()'s second argument is the
total size of the buffer, not the size of the buffer minus the offset.
Since simple_write_to_buffer() accounts for the offset in its
implementation, snapshot_write() can just pass the full page size
directly down.

Signed-off-by: Evan Green <evgreen@...omium.org>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 kernel/power/user.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/power/user.c b/kernel/power/user.c
index f83c1876b39c0..67659e507747e 100644
--- a/kernel/power/user.c
+++ b/kernel/power/user.c
@@ -181,7 +181,7 @@ static ssize_t snapshot_write(struct file *filp, const char __user *buf,
 		if (res <= 0)
 			goto unlock;
 	} else {
-		res = PAGE_SIZE - pg_offp;
+		res = PAGE_SIZE;
 	}

 	if (!data_of(data->handle)) {
-- 
2.33.0