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authorGaurav Kohli <gkohli@codeaurora.org>2018-01-23 13:16:34 +0530
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>2018-02-03 17:39:19 +0100
commit3c538ad935465d7ba4bf0b5747fadcfdf05311c9 (patch)
parenteb6de1af2e7235133a0e2563c09926ca28361095 (diff)
tty: fix data race between tty_init_dev and flush of buf
commit b027e2298bd588d6fa36ed2eda97447fb3eac078 upstream. There can be a race, if receive_buf call comes before tty initialization completes in n_tty_open and tty->disc_data may be NULL. CPU0 CPU1 ---- ---- 000|n_tty_receive_buf_common() n_tty_open() -001|n_tty_receive_buf2() tty_ldisc_open.isra.3() -002|tty_ldisc_receive_buf(inline) tty_ldisc_setup() Using ldisc semaphore lock in tty_init_dev till disc_data initializes completely. Signed-off-by: Gaurav Kohli <gkohli@codeaurora.org> Reviewed-by: Alan Cox <alan@linux.intel.com> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
3 files changed, 11 insertions, 3 deletions
diff --git a/drivers/tty/tty_io.c b/drivers/tty/tty_io.c
index 94cccb6efa32..7892d0be8af9 100644
--- a/drivers/tty/tty_io.c
+++ b/drivers/tty/tty_io.c
@@ -1322,6 +1322,9 @@ struct tty_struct *tty_init_dev(struct tty_driver *driver, int idx)
"%s: %s driver does not set tty->port. This will crash the kernel later. Fix the driver!\n",
__func__, tty->driver->name);
+ retval = tty_ldisc_lock(tty, 5 * HZ);
+ if (retval)
+ goto err_release_lock;
tty->port->itty = tty;
@@ -1332,6 +1335,7 @@ struct tty_struct *tty_init_dev(struct tty_driver *driver, int idx)
retval = tty_ldisc_setup(tty, tty->link);
if (retval)
goto err_release_tty;
+ tty_ldisc_unlock(tty);
/* Return the tty locked so that it cannot vanish under the caller */
return tty;
@@ -1344,9 +1348,11 @@ err_module_put:
/* call the tty release_tty routine to clean out this slot */
- tty_unlock(tty);
+ tty_ldisc_unlock(tty);
tty_info_ratelimited(tty, "ldisc open failed (%d), clearing slot %d\n",
retval, idx);
+ tty_unlock(tty);
release_tty(tty, idx);
return ERR_PTR(retval);
diff --git a/drivers/tty/tty_ldisc.c b/drivers/tty/tty_ldisc.c
index 84a8ac2a779f..7c895684c3ef 100644
--- a/drivers/tty/tty_ldisc.c
+++ b/drivers/tty/tty_ldisc.c
@@ -336,7 +336,7 @@ static inline void __tty_ldisc_unlock(struct tty_struct *tty)
-static int tty_ldisc_lock(struct tty_struct *tty, unsigned long timeout)
+int tty_ldisc_lock(struct tty_struct *tty, unsigned long timeout)
int ret;
@@ -347,7 +347,7 @@ static int tty_ldisc_lock(struct tty_struct *tty, unsigned long timeout)
return 0;
-static void tty_ldisc_unlock(struct tty_struct *tty)
+void tty_ldisc_unlock(struct tty_struct *tty)
clear_bit(TTY_LDISC_HALTED, &tty->flags);
diff --git a/include/linux/tty.h b/include/linux/tty.h
index 7ac8ba208b1f..0a6c71e0ad01 100644
--- a/include/linux/tty.h
+++ b/include/linux/tty.h
@@ -405,6 +405,8 @@ extern const char *tty_name(const struct tty_struct *tty);
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);
+extern int tty_ldisc_lock(struct tty_struct *tty, unsigned long timeout);
+extern void tty_ldisc_unlock(struct tty_struct *tty);
static inline void tty_kref_put(struct tty_struct *tty)
{ }