2020-06-13 12:53:52

by Xiyu Yang

Subject: [PATCH] tty: serial_core: Fix uart_state leak when port shutdown

uart_shutdown() invokes uart_port_lock(), which returns a reference of
the uart_port object if increases the refcount of the uart_state object
successfully or returns NULL if fails.

However, uart_shutdown() don't take the return value of uart_port_lock()
as the new uart_port object to "uport" and use the old "uport" instead
to balance refcount in uart_port_unlock(), which may cause a redundant
decrement of refcount occurred when the new "uport" equals to NULL and
then cause a potential memory leak.

Fix this issue by update the "uport" object to the return value of
uart_port_lock() when invoking uart_port_lock().

Signed-off-by: Xiyu Yang <[email protected]>
Signed-off-by: Xin Tan <[email protected]>
---
drivers/tty/serial/serial_core.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/tty/serial/serial_core.c b/drivers/tty/serial/serial_core.c
index 57840cf90388..ab8756ef2b60 100644
--- a/drivers/tty/serial/serial_core.c
+++ b/drivers/tty/serial/serial_core.c
@@ -313,7 +313,7 @@ static void uart_shutdown(struct tty_struct *tty, struct uart_state *state)
* console driver may need to allocate/free a debug object, which
* can endup in printk() recursion.
*/
- uart_port_lock(state, flags);
+ uport = uart_port_lock(state, flags);
xmit_buf = state->xmit.buf;
state->xmit.buf = NULL;
uart_port_unlock(uport, flags);
--
2.7.4

2020-06-15 05:02:18

by Jiri Slaby

Subject: Re: [PATCH] tty: serial_core: Fix uart_state leak when port shutdown

On 13. 06. 20, 14:51, Xiyu Yang wrote:
> uart_shutdown() invokes uart_port_lock(), which returns a reference of
> the uart_port object if increases the refcount of the uart_state object
> successfully or returns NULL if fails.
>
> However, uart_shutdown() don't take the return value of uart_port_lock()
> as the new uart_port object to "uport" and use the old "uport" instead
> to balance refcount in uart_port_unlock(), which may cause a redundant
> decrement of refcount occurred when the new "uport" equals to NULL and
> then cause a potential memory leak.

uport should be valid at that point and both the returned one and the
used one should be the same.

> Fix this issue by update the "uport" object to the return value of
> uart_port_lock() when invoking uart_port_lock().

Do you actually encounter the issue or is this some static analyzer result?

> Signed-off-by: Xiyu Yang <[email protected]>
> Signed-off-by: Xin Tan <[email protected]>
> ---
> drivers/tty/serial/serial_core.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/drivers/tty/serial/serial_core.c b/drivers/tty/serial/serial_core.c
> index 57840cf90388..ab8756ef2b60 100644
> --- a/drivers/tty/serial/serial_core.c
> +++ b/drivers/tty/serial/serial_core.c
> @@ -313,7 +313,7 @@ static void uart_shutdown(struct tty_struct *tty, struct uart_state *state)
> * console driver may need to allocate/free a debug object, which
> * can endup in printk() recursion.
> */
> - uart_port_lock(state, flags);
> + uport = uart_port_lock(state, flags);
> xmit_buf = state->xmit.buf;
> state->xmit.buf = NULL;
> uart_port_unlock(uport, flags);
>

thanks,
--
js
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