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authorOkash Khawaja <okash.khawaja@gmail.com>2017-07-20 08:22:36 +0100
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>2017-08-28 16:15:41 +0200
commita09ac3974d0c0b25dfa70f8076546bc4876dd7a8 (patch)
tree54ceaea718b5ceb2cdaaaae1a1f175f186e80be7 /include/linux/tty.h
parent8439a69e72888daa7d2667980efaf20d8bbe7b20 (diff)
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tty: resolve tty contention between kernel and user space
The commit 12e84c71b7d4 ("tty: export tty_open_by_driver") exports tty_open_by_device to allow tty to be opened from inside kernel which works fine except that it doesn't handle contention with user space or another kernel-space open of the same tty. For example, opening a tty from user space while it is kernel opened results in failure and a kernel log message about mismatch between tty->count and tty's file open count. This patch makes kernel access to tty exclusive, so that if a user process or kernel opens a kernel opened tty, it gets -EBUSY. It does this by adding TTY_KOPENED flag to tty->flags. When this flag is set, tty_open_by_driver returns -EBUSY. Instead of overloading tty_open_by_driver for both kernel and user space, this patch creates a separate function tty_kopen which closely follows tty_open_by_driver. tty_kclose closes the tty opened by tty_kopen. To address the mismatch between tty->count and #fd's, this patch adds #kopen's to the count before comparing it with tty->count. That way check_tty_count reflects correct usage count. Returning -EBUSY on tty open is a change in the interface. I have tested this with minicom, picocom and commands like "echo foo > /dev/ttyS0". They all correctly report "Device or resource busy" when the tty is already kernel opened. Signed-off-by: Okash Khawaja <okash.khawaja@gmail.com> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Diffstat (limited to 'include/linux/tty.h')
-rw-r--r--include/linux/tty.h21
1 files changed, 21 insertions, 0 deletions
diff --git a/include/linux/tty.h b/include/linux/tty.h
index 79c30daf46a9..236d52b8be8c 100644
--- a/include/linux/tty.h
+++ b/include/linux/tty.h
@@ -261,6 +261,8 @@ struct tty_port {
*/
#define TTY_PORT_CTS_FLOW 3 /* h/w flow control enabled */
#define TTY_PORT_CHECK_CD 4 /* carrier detect enabled */
+#define TTY_PORT_KOPENED 5 /* device exclusively opened by
+ kernel */
/*
* Where all of the state associated with a tty is kept while the tty
@@ -401,6 +403,8 @@ extern int __init tty_init(void);
extern const char *tty_name(const struct tty_struct *tty);
extern struct tty_struct *tty_open_by_driver(dev_t device, struct inode *inode,
struct file *filp);
+extern struct tty_struct *tty_kopen(dev_t device);
+extern void tty_kclose(struct tty_struct *tty);
extern int tty_dev_name_to_number(const char *name, dev_t *number);
#else
static inline void tty_kref_put(struct tty_struct *tty)
@@ -425,6 +429,10 @@ static inline const char *tty_name(const struct tty_struct *tty)
static inline struct tty_struct *tty_open_by_driver(dev_t device,
struct inode *inode, struct file *filp)
{ return NULL; }
+static inline struct tty_struct *tty_kopen(dev_t device)
+{ return ERR_PTR(-ENODEV); }
+static inline void tty_kclose(struct tty_struct *tty)
+{ }
static inline int tty_dev_name_to_number(const char *name, dev_t *number)
{ return -ENOTSUPP; }
#endif
@@ -652,6 +660,19 @@ static inline void tty_port_set_initialized(struct tty_port *port, bool val)
clear_bit(TTY_PORT_INITIALIZED, &port->iflags);
}
+static inline bool tty_port_kopened(struct tty_port *port)
+{
+ return test_bit(TTY_PORT_KOPENED, &port->iflags);
+}
+
+static inline void tty_port_set_kopened(struct tty_port *port, bool val)
+{
+ if (val)
+ set_bit(TTY_PORT_KOPENED, &port->iflags);
+ else
+ clear_bit(TTY_PORT_KOPENED, &port->iflags);
+}
+
extern struct tty_struct *tty_port_tty_get(struct tty_port *port);
extern void tty_port_tty_set(struct tty_port *port, struct tty_struct *tty);
extern int tty_port_carrier_raised(struct tty_port *port);