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Subject[PATCH 05/23] fs: check FMODE_WRITE in __kernel_write
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 <>
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;

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