diff options
| author | Okash Khawaja <okash.khawaja@gmail.com> | 2017-07-20 08:22:36 +0100 |
|---|---|---|
| committer | Greg Kroah-Hartman <gregkh@linuxfoundation.org> | 2017-08-28 16:15:41 +0200 |
| commit | a09ac3974d0c0b25dfa70f8076546bc4876dd7a8 (patch) | |
| tree | 54ceaea718b5ceb2cdaaaae1a1f175f186e80be7 /include/linux/tty.h | |
| parent | 8439a69e72888daa7d2667980efaf20d8bbe7b20 (diff) | |
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.h | 21 |
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); |