@@ -753,6 +753,15 @@ static ssize_t uhid_char_write(struct file *file, const char __user *buffer,
return ret ? ret : count;
}
+static ssize_t uhid_char_splice_write(struct pipe_inode_info *pipe,
+ struct file *out,
+ loff_t *ppos,
+ size_t len,
+ unsigned int flags)
+{
+ return -EOPNOTSUPP;
+}
+
static __poll_t uhid_char_poll(struct file *file, poll_table *wait)
{
struct uhid_device *uhid = file->private_data;
@@ -771,6 +780,7 @@ static const struct file_operations uhid_fops = {
.release = uhid_char_release,
.read = uhid_char_read,
.write = uhid_char_write,
+ .splice_write = uhid_char_splice_write,
.poll = uhid_char_poll,
.llseek = no_llseek,
};
The kernel has a default implementation of splice(2) for writing from a pipe into an arbitrary file. This behavior can be overriden by providing an f_op.splice_write() callback. Unfortunately, the default implementation of splice_write() takes page by page from the source pipe, calls kmap() and passes the mapped page as kernel-address to f_op.write(). Thus, it uses standard write(2) to implement splice(2). However, since the page is kernel-mapped, they have to `set_fs(get_ds())`. This is mostly fine, but UHID takes command-streams through write(2), and thus it might interpret the data taken as pointers. If called with KERNEL_DS, you can trick UHID to allow kernel-space pointers as well. As a simple fix, prevent splice(2) on UHID. It is unsecure, but it is also non-functional. We need a linear mapping of the input in UHID, so chunked input from splice(2) makes no sense, anyway. Reported-by: syzbot+72473edc9bf4eb1c6556@syzkaller.appspotmail.com Signed-off-by: David Herrmann <dh.herrmann@gmail.com> --- drivers/hid/uhid.c | 10 ++++++++++ 1 file changed, 10 insertions(+)