From a09ac3974d0c0b25dfa70f8076546bc4876dd7a8 Mon Sep 17 00:00:00 2001 From: Okash Khawaja Date: Thu, 20 Jul 2017 08:22:36 +0100 Subject: 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 Signed-off-by: Greg Kroah-Hartman --- include/linux/tty.h | 21 +++++++++++++++++++++ 1 file changed, 21 insertions(+) (limited to 'include/linux/tty.h') 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); -- cgit v1.2.3 From a033c3b10a2bec387ccd9e39fadd94eef6519626 Mon Sep 17 00:00:00 2001 From: Okash Khawaja Date: Thu, 20 Jul 2017 08:22:38 +0100 Subject: tty: undo export of tty_open_by_driver Since we have tty_kopen, we no longer need to export tty_open_by_driver. This patch makes this function static. Signed-off-by: Okash Khawaja Signed-off-by: Greg Kroah-Hartman --- drivers/tty/tty_io.c | 3 +-- include/linux/tty.h | 5 ----- 2 files changed, 1 insertion(+), 7 deletions(-) (limited to 'include/linux/tty.h') diff --git a/drivers/tty/tty_io.c b/drivers/tty/tty_io.c index b03504d4916e..195290f3803a 100644 --- a/drivers/tty/tty_io.c +++ b/drivers/tty/tty_io.c @@ -1885,7 +1885,7 @@ EXPORT_SYMBOL_GPL(tty_kopen); * - concurrent tty driver removal w/ lookup * - concurrent tty removal from driver table */ -struct tty_struct *tty_open_by_driver(dev_t device, struct inode *inode, +static struct tty_struct *tty_open_by_driver(dev_t device, struct inode *inode, struct file *filp) { struct tty_struct *tty; @@ -1936,7 +1936,6 @@ out: tty_driver_kref_put(driver); return tty; } -EXPORT_SYMBOL_GPL(tty_open_by_driver); /** * tty_open - open a tty device diff --git a/include/linux/tty.h b/include/linux/tty.h index 236d52b8be8c..cf53eb539f6e 100644 --- a/include/linux/tty.h +++ b/include/linux/tty.h @@ -401,8 +401,6 @@ extern struct tty_struct *get_current_tty(void); /* tty_io.c */ 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); @@ -426,9 +424,6 @@ static inline int __init tty_init(void) { return 0; } static inline const char *tty_name(const struct tty_struct *tty) { return "(none)"; } -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) -- cgit v1.2.3