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From:   Nicolas Boichat <drinkcat@chromium.org>
To:     "Darrick J . Wong" <djwong@kernel.org>
Cc:     Alexander Viro <viro@zeniv.linux.org.uk>,
        Ian Lance Taylor <iant@google.com>,
        Luis Lozano <llozano@chromium.org>,
        Greg KH <gregkh@linuxfoundation.org>,
        Dave Chinner <david@fromorbit.com>,
        Nicolas Boichat <drinkcat@chromium.org>,
        linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: [PATCH 6/6] vfs: Disallow copy_file_range on generated file systems
Date:   Fri, 12 Feb 2021 12:44:05 +0800
Message-Id: <20210212124354.6.Idc9c3110d708aa0df9d8fe5a6246524dc8469dae@changeid>
In-Reply-To: <20210212044405.4120619-1-drinkcat@chromium.org>
References: <20210212044405.4120619-1-drinkcat@chromium.org>
MIME-Version: 1.0
Content-Transfer-Encoding: 8bit
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copy_file_range (which calls generic_copy_file_checks) uses the
inode file size to adjust the copy count parameter. This breaks
with special filesystems like procfs/sysfs/debugfs/tracefs, where
the file size appears to be zero, but content is actually returned
when a read operation is performed. Other issues would also
happen on partial writes, as the function would attempt to seek
in the input file.

Use the newly introduced FS_GENERATED_CONTENT filesystem flag
to return -EOPNOTSUPP: applications can then retry with a more
usual read/write based file copy (the fallback code is usually
already present to handle older kernels).

Signed-off-by: Nicolas Boichat <drinkcat@chromium.org>
---

 fs/read_write.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/fs/read_write.c b/fs/read_write.c
index 0029ff2b0ca8..80322e89fb0a 100644
--- a/fs/read_write.c
+++ b/fs/read_write.c
@@ -1485,6 +1485,9 @@ ssize_t vfs_copy_file_range(struct file *file_in, loff_t pos_in,
 	if (flags != 0)
 		return -EINVAL;
 
+	if (file_inode(file_in)->i_sb->s_type->fs_flags & FS_GENERATED_CONTENT)
+		return -EOPNOTSUPP;
+
 	ret = generic_copy_file_checks(file_in, pos_in, file_out, pos_out, &len,
 				       flags);
 	if (unlikely(ret))
-- 
2.30.0.478.g8a0d178c01-goog