[PATCH v2 0/2] tty: erase buffers when the kernel is done with it.

[PATCH v2 0/2] tty: erase buffers when the kernel is done with it.

[Greg Kroah-Hartman]

azlig and Milan Broz reported that when the tty layer is done with a
buffer, the data can hang around in it for a very long time.  That
sometimes can "leak" to userspace under some conditions.

Because of this, just zero out the data after the tty layer is finished
with it, for buffers that we "think" should be zeroed out.

v2 - addressed some review comments on the 2/2 patch.

Greg Kroah-Hartman (1):
  tty: wipe buffer if not echoing data

Linus Torvalds (1):
  tty: wipe buffer.

 drivers/tty/n_tty.c      | 20 +++++++++++++++++---
 drivers/tty/tty_buffer.c |  6 +++++-
 2 files changed, 22 insertions(+), 4 deletions(-)

-- 
2.19.0

[PATCH v2 1/2] tty: wipe buffer.

[Greg Kroah-Hartman]

From: Linus Torvalds <torvalds@linux-foundation.org>

After we are done with the tty buffer, zero it out.

Reported-by: aszlig <aszlig@nix.build>
Tested-by: Milan Broz <gmazyland@gmail.com>
Tested-by: aszlig <aszlig@nix.build>
Cc: Willy Tarreau <w@1wt.eu>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
v2 - no change

 drivers/tty/tty_buffer.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/drivers/tty/tty_buffer.c b/drivers/tty/tty_buffer.c
index c996b6859c5e..ae3ce330200e 100644
--- a/drivers/tty/tty_buffer.c
+++ b/drivers/tty/tty_buffer.c
@@ -468,11 +468,15 @@ receive_buf(struct tty_port *port, struct tty_buffer *head, int count)
 {
 	unsigned char *p = char_buf_ptr(head, head->read);
 	char	      *f = NULL;
+	int n;
 
 	if (~head->flags & TTYB_NORMAL)
 		f = flag_buf_ptr(head, head->read);
 
-	return port->client_ops->receive_buf(port, p, f, count);
+	n = port->client_ops->receive_buf(port, p, f, count);
+	if (n > 0)
+		memset(p, 0, n);
+	return n;
 }
 
 /**
-- 
2.19.0

[PATCH v2 2/2] tty: wipe buffer if not echoing data

[Greg Kroah-Hartman]

From: Greg KH <greg@kroah.com>

If we are not echoing the data to userspace or the console is in icanon
mode, then perhaps it is a "secret" so we should wipe it once we are
done with it.

This mirrors the logic that the audit code has.

Reported-by: aszlig <aszlig@nix.build>
Tested-by: Milan Broz <gmazyland@gmail.com>
Tested-by: aszlig <aszlig@nix.build>
Cc: Willy Tarreau <w@1wt.eu>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
v2 - update changelog comment to mention icanon
     address the fact that copy_to_user() might not copy the whole buffer

 drivers/tty/n_tty.c | 20 +++++++++++++++++---
 1 file changed, 17 insertions(+), 3 deletions(-)

diff --git a/drivers/tty/n_tty.c b/drivers/tty/n_tty.c
index 431742201709..3ad460219fd6 100644
--- a/drivers/tty/n_tty.c
+++ b/drivers/tty/n_tty.c
@@ -152,17 +152,28 @@ static inline unsigned char *echo_buf_addr(struct n_tty_data *ldata, size_t i)
 	return &ldata->echo_buf[i & (N_TTY_BUF_SIZE - 1)];
 }
 
+/* If we are not echoing the data, perhaps this is a secret so erase it */
+static void zero_buffer(struct tty_struct *tty, u8 *buffer, int size)
+{
+	bool icanon = !!L_ICANON(tty);
+	bool no_echo = !L_ECHO(tty);
+
+	if (icanon && no_echo)
+		memset(buffer, 0x00, size);
+}
+
 static int tty_copy_to_user(struct tty_struct *tty, void __user *to,
 			    size_t tail, size_t n)
 {
 	struct n_tty_data *ldata = tty->disc_data;
 	size_t size = N_TTY_BUF_SIZE - tail;
-	const void *from = read_buf_addr(ldata, tail);
+	void *from = read_buf_addr(ldata, tail);
 	int uncopied;
 
 	if (n > size) {
 		tty_audit_add_data(tty, from, size);
 		uncopied = copy_to_user(to, from, size);
+		zero_buffer(tty, from, size - uncopied);
 		if (uncopied)
 			return uncopied;
 		to += size;
@@ -171,7 +182,9 @@ static int tty_copy_to_user(struct tty_struct *tty, void __user *to,
 	}
 
 	tty_audit_add_data(tty, from, n);
-	return copy_to_user(to, from, n);
+	uncopied = copy_to_user(to, from, n);
+	zero_buffer(tty, from, n - uncopied);
+	return uncopied;
 }
 
 /**
@@ -1960,11 +1973,12 @@ static int copy_from_read_buf(struct tty_struct *tty,
 	n = min(head - ldata->read_tail, N_TTY_BUF_SIZE - tail);
 	n = min(*nr, n);
 	if (n) {
-		const unsigned char *from = read_buf_addr(ldata, tail);
+		unsigned char *from = read_buf_addr(ldata, tail);
 		retval = copy_to_user(*b, from, n);
 		n -= retval;
 		is_eof = n == 1 && *from == EOF_CHAR(tty);
 		tty_audit_add_data(tty, from, n);
+		zero_buffer(tty, from, n);
 		smp_store_release(&ldata->read_tail, ldata->read_tail + n);
 		/* Turn single EOF into zero-length read */
 		if (L_EXTPROC(tty) && ldata->icanon && is_eof &&
-- 
2.19.0

Re: [PATCH v2 0/2] tty: erase buffers when the kernel is done with it.

[Milan Broz]

On 04/10/2018 20:06, Greg Kroah-Hartman wrote:
> azlig and Milan Broz reported that when the tty layer is done with a
> buffer, the data can hang around in it for a very long time.  That
> sometimes can "leak" to userspace under some conditions.
> 
> Because of this, just zero out the data after the tty layer is finished
> with it, for buffers that we "think" should be zeroed out.
> 
> v2 - addressed some review comments on the 2/2 patch.

Hello Greg,

together with our intern we re-tested both patches and it fixes the reported problem,
so, if it helps anything, you can add

Tested-by: Milan Broz <gmazyland@gmail.com>
Tested-by: Daniel Zatovic <daniel.zatovic@gmail.com>

Do you plan to add this to linux-next?

Thanks!
Milan

> 
> Greg Kroah-Hartman (1):
>   tty: wipe buffer if not echoing data
> 
> Linus Torvalds (1):
>   tty: wipe buffer.
> 
>  drivers/tty/n_tty.c      | 20 +++++++++++++++++---
>  drivers/tty/tty_buffer.c |  6 +++++-
>  2 files changed, 22 insertions(+), 4 deletions(-)
> 

Re: [PATCH v2 0/2] tty: erase buffers when the kernel is done with it.

[Greg Kroah-Hartman]

On Wed, Oct 10, 2018 at 08:20:06PM +0200, Milan Broz wrote:
> On 04/10/2018 20:06, Greg Kroah-Hartman wrote:
> > azlig and Milan Broz reported that when the tty layer is done with a
> > buffer, the data can hang around in it for a very long time.  That
> > sometimes can "leak" to userspace under some conditions.
> > 
> > Because of this, just zero out the data after the tty layer is finished
> > with it, for buffers that we "think" should be zeroed out.
> > 
> > v2 - addressed some review comments on the 2/2 patch.
> 
> Hello Greg,
> 
> together with our intern we re-tested both patches and it fixes the reported problem,
> so, if it helps anything, you can add
> 
> Tested-by: Milan Broz <gmazyland@gmail.com>
> Tested-by: Daniel Zatovic <daniel.zatovic@gmail.com>
> 
> Do you plan to add this to linux-next?

Yes, I'll queue it up soon, thanks for testing!

greg k-h