archive mirror
 help / color / mirror / Atom feed
* [PATCH] HID: uhid: prevent splice(2)
@ 2018-11-14 13:07 David Herrmann
  0 siblings, 0 replies; only message in thread
From: David Herrmann @ 2018-11-14 13:07 UTC (permalink / raw)
  To: linux-input; +Cc: linux-kernel, jikos, benjamin.tissoires, David Herrmann

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.

Signed-off-by: David Herrmann <>
 drivers/hid/uhid.c | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/drivers/hid/uhid.c b/drivers/hid/uhid.c
index 3c5507313606..fefedc0b4dc6 100644
--- a/drivers/hid/uhid.c
+++ b/drivers/hid/uhid.c
@@ -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,

^ permalink raw reply	[flat|nested] only message in thread

only message in thread, other threads:[~2018-11-14 13:07 UTC | newest]

Thread overview: (only message) (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2018-11-14 13:07 [PATCH] HID: uhid: prevent splice(2) David Herrmann

This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).