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From:   Christoph Hellwig <hch@lst.de>
To:     Al Viro <viro@zeniv.linux.org.uk>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Stephen Rothwell <sfr@canb.auug.org.au>
Cc:     Luis Chamberlain <mcgrof@kernel.org>,
        Matthew Wilcox <willy@infradead.org>,
        Kees Cook <keescook@chromium.org>,
        Iurii Zaikin <yzaikin@google.com>,
        linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org
Subject: [PATCH 05/23] fs: check FMODE_WRITE in __kernel_write
Date:   Tue,  7 Jul 2020 19:47:43 +0200
Message-Id: <20200707174801.4162712-6-hch@lst.de>
In-Reply-To: <20200707174801.4162712-1-hch@lst.de>
References: <20200707174801.4162712-1-hch@lst.de>
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Add a WARN_ON_ONCE if the file isn't actually open for write.  This
matches the check done in vfs_write, but actually warn warns as a
kernel user calling write on a file not opened for writing is a pretty
obvious programming error.

Signed-off-by: Christoph Hellwig <hch@lst.de>
---
 fs/read_write.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/fs/read_write.c b/fs/read_write.c
index 2c601d853ff3d8..8f9fc05990ae8b 100644
--- a/fs/read_write.c
+++ b/fs/read_write.c
@@ -505,6 +505,8 @@ ssize_t __kernel_write(struct file *file, const void *buf, size_t count, loff_t
 	const char __user *p;
 	ssize_t ret;
 
+	if (WARN_ON_ONCE(!(file->f_mode & FMODE_WRITE)))
+		return -EBADF;
 	if (!(file->f_mode & FMODE_CAN_WRITE))
 		return -EINVAL;
 
-- 
2.26.2