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SubjectRe: tty_[un]register_devfs putting 3K structures on the stack
Date
From
tytso@mit.edu said:
> If the problem only impacts User-mode Linux, it's hard for me to justify
> hanging the "critical" label on it. However I'm willing to look at the
> patch, bless it, and send it on to Linus

Below is the patch to rid tty_register_devfs and tty_unregister_devfs of the
tty_struct local.

I still think that treating it as critical deserves consideration because it's
a potentially nasty problem, and one that could be tough to debug. As Alan
pointed out, it's easier to fix the bug than it is to prove that it can't
happen on any of the other arches.

Jeff

diff -u drivers/char/tty_io.c.orig drivers/char/tty_io.c
--- drivers/char/tty_io.c.orig Tue Oct 17 00:06:04 2000
+++ drivers/char/tty_io.c Tue Oct 17 00:05:37 2000
@@ -1994,12 +1994,11 @@
{
#ifdef CONFIG_DEVFS_FS
umode_t mode = S_IFCHR | S_IRUSR | S_IWUSR;
- struct tty_struct tty;
+ kdev_t device = MKDEV (driver->major, minor);
+ int idx = minor - driver->minor_start;
char buf[32];

- tty.driver = *driver;
- tty.device = MKDEV (driver->major, minor);
- switch (tty.device) {
+ switch (device) {
case TTY_DEV:
case PTMX_DEV:
mode |= S_IRGRP | S_IWGRP | S_IROTH | S_IWOTH;
@@ -2020,23 +2019,21 @@
(driver->major < UNIX98_PTY_SLAVE_MAJOR + UNIX98_NR_MAJORS) )
flags |= DEVFS_FL_CURRENT_OWNER;
# endif
- devfs_register (NULL, tty_name (&tty, buf), flags | DEVFS_FL_DEFAULT,
+ sprintf(buf, driver->name, idx + driver->name_base);
+ devfs_register (NULL, buf, flags | DEVFS_FL_DEFAULT,
driver->major, minor, mode, &tty_fops, NULL);
#endif /* CONFIG_DEVFS_FS */
}

-void tty_unregister_devfs (struct tty_driver *driver, unsigned minor)
+void tty_unregister_devfs (struct tty_driver *driver, unsigned int minor)
{
#ifdef CONFIG_DEVFS_FS
void * handle;
- struct tty_struct tty;
+ int idx = minor - driver->minor_start;
char buf[32];

- tty.driver = *driver;
- tty.device = MKDEV(driver->major, minor);
-
- handle = devfs_find_handle (NULL, tty_name (&tty, buf),
- driver->major, minor,
+ sprintf(buf, driver->name, idx + driver->name_base);
+ handle = devfs_find_handle (NULL, buf, driver->major, minor,
DEVFS_SPECIAL_CHR, 0);
devfs_unregister (handle);
#endif /* CONFIG_DEVFS_FS */

-
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