linux-stable.git/drivers/tty/tty_ldisc.c, branch linux-5.4.y

tty: ldsic: fix tty_ldisc_autoload sysctl's proc_handler

2024-12-14T18:44:36+00:00

commit 635a9fca54f4f4148be1ae1c7c6bd37af80f5773 upstream.

Commit 7c0cca7c847e ("tty: ldisc: add sysctl to prevent autoloading of
ldiscs") introduces the tty_ldisc_autoload sysctl with the wrong
proc_handler. .extra1 and .extra2 parameters are set to avoid other values
thant SYSCTL_ZERO or SYSCTL_ONE to be set but proc_dointvec do not uses
them.

This commit fixes this by using proc_dointvec_minmax instead of
proc_dointvec.

Fixes: 7c0cca7c847e ("tty: ldisc: add sysctl to prevent autoloading of ldiscs")
Cc: stable 
Signed-off-by: Nicolas Bouchinet 
Reviewed-by: Lin Feng 
Reviewed-by: Jiri Slaby 
Link: https://lore.kernel.org/r/20241112131357.49582-4-nicolas.bouchinet@clip-os.org
Signed-off-by: Greg Kroah-Hartman 
Signed-off-by: Greg Kroah-Hartman

proc/sysctl: add shared variables for range check

2019-07-19T00:08:07+00:00

In the sysctl code the proc_dointvec_minmax() function is often used to
validate the user supplied value between an allowed range.  This
function uses the extra1 and extra2 members from struct ctl_table as
minimum and maximum allowed value.

On sysctl handler declaration, in every source file there are some
readonly variables containing just an integer which address is assigned
to the extra1 and extra2 members, so the sysctl range is enforced.

The special values 0, 1 and INT_MAX are very often used as range
boundary, leading duplication of variables like zero=0, one=1,
int_max=INT_MAX in different source files:

    $ git grep -E '\.extra[12].*&(zero|one|int_max)' |wc -l
    248

Add a const int array containing the most commonly used values, some
macros to refer more easily to the correct array member, and use them
instead of creating a local one for every object file.

This is the bloat-o-meter output comparing the old and new binary
compiled with the default Fedora config:

    # scripts/bloat-o-meter -d vmlinux.o.old vmlinux.o
    add/remove: 2/2 grow/shrink: 0/2 up/down: 24/-188 (-164)
    Data                                         old     new   delta
    sysctl_vals                                    -      12     +12
    __kstrtab_sysctl_vals                          -      12     +12
    max                                           14      10      -4
    int_max                                       16       -     -16
    one                                           68       -     -68
    zero                                         128      28    -100
    Total: Before=20583249, After=20583085, chg -0.00%

[mcroce@redhat.com: tipc: remove two unused variables]
  Link: http://lkml.kernel.org/r/20190530091952.4108-1-mcroce@redhat.com
[akpm@linux-foundation.org: fix net/ipv6/sysctl_net_ipv6.c]
[arnd@arndb.de: proc/sysctl: make firmware loader table conditional]
  Link: http://lkml.kernel.org/r/20190617130014.1713870-1-arnd@arndb.de
[akpm@linux-foundation.org: fix fs/eventpoll.c]
Link: http://lkml.kernel.org/r/20190430180111.10688-1-mcroce@redhat.com
Signed-off-by: Matteo Croce 
Signed-off-by: Arnd Bergmann 
Acked-by: Kees Cook 
Reviewed-by: Aaron Tomlin 
Cc: Matthew Wilcox 
Cc: Stephen Rothwell 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

locking/lockdep: Rename lockdep_assert_held_exclusive() -> lockdep_assert_held_write()

2019-06-17T10:09:24+00:00

All callers of lockdep_assert_held_exclusive() use it to verify the
correct locking state of either a semaphore (ldisc_sem in tty,
mmap_sem for perf events, i_rwsem of inode for dax) or rwlock by
apparmor. Thus it makes sense to rename _exclusive to _write since
that's the semantics callers care. Additionally there is already
lockdep_assert_held_read(), which this new naming is more consistent with.

No functional changes.

Signed-off-by: Nikolay Borisov 
Signed-off-by: Peter Zijlstra (Intel) 
Cc: Linus Torvalds 
Cc: Peter Zijlstra 
Cc: Thomas Gleixner 
Link: https://lkml.kernel.org/r/20190531100651.3969-1-nborisov@suse.com
Signed-off-by: Ingo Molnar

tty: ldisc: add sysctl to prevent autoloading of ldiscs

2019-01-30T08:31:30+00:00

By default, the kernel will automatically load the module of any line
dicipline that is asked for.  As this sometimes isn't the safest thing
to do, provide a sysctl to disable this feature.

By default, we set this to 'y' as that is the historical way that Linux
has worked, and we do not want to break working systems.  But in the
future, perhaps this can default to 'n' to prevent this functionality.

Signed-off-by: Greg Kroah-Hartman 
Reviewed-by: Theodore Ts'o 
Signed-off-by: Greg Kroah-Hartman

tty/ldsem: Add lockdep asserts for ldisc_sem

2018-12-05T11:16:33+00:00

Make sure under CONFIG_LOCKDEP that each change to line discipline
is done with held write semaphor.
Otherwise potential reader will have a good time dereferencing
incomplete/uninitialized ldisc.

An exception here is tty_ldisc_open(), as it's called without ldisc_sem
locked by tty_init_dev() => tty_ldisc_setup() for the tty->link.

It seem valid as tty_init_dev() will call tty_driver_install_tty()
which will find ops->install(). Install will establish tty->link in
pty_common_install(), just after allocation of slave tty with
alloc_tty_struct(). So, no one should have a reference to slave pty yet.

Cc: Jiri Slaby 
Cc: Peter Zijlstra 
Signed-off-by: Dmitry Safonov 
Signed-off-by: Greg Kroah-Hartman

tty: Don't block on IO when ldisc change is pending

2018-12-05T11:16:33+00:00

There might be situations where tty_ldisc_lock() has blocked, but there
is already IO on tty and it prevents line discipline changes.
It might theoretically turn into dead-lock.

Basically, provide more priority to pending tty_ldisc_lock() than to
servicing reads/writes over tty.

User-visible issue was reported by Mikulas where on pa-risc with
Debian 5 reboot took either 80 seconds, 3 minutes or 3:25 after proper
locking in tty_reopen().

Cc: Jiri Slaby 
Reported-by: Mikulas Patocka 
Signed-off-by: Dmitry Safonov 
Signed-off-by: Greg Kroah-Hartman

proc: introduce proc_create_seq{,_data}

2018-05-16T05:23:35+00:00

Variants of proc_create{,_data} that directly take a struct seq_operations
argument and drastically reduces the boilerplate code in the callers.

All trivial callers converted over.

Signed-off-by: Christoph Hellwig

tty: Use __GFP_NOFAIL for tty_ldisc_get()

2018-04-25T13:03:44+00:00

syzbot is reporting crashes triggered by memory allocation fault injection
at tty_ldisc_get() [1]. As an attempt to handle OOM in a graceful way, we
have tried commit 5362544bebe85071 ("tty: don't panic on OOM in
tty_set_ldisc()"). But we reverted that attempt by commit a8983d01f9b7d600
("Revert "tty: don't panic on OOM in tty_set_ldisc()"") due to reproducible
crash. We should spend resource for finding and fixing race condition bugs
rather than complicate error paths for 2 * sizeof(void *) bytes allocation
failure.

[1] https://syzkaller.appspot.com/bug?id=489d33fa386453859ead58ff5171d43772b13aa3

Signed-off-by: Tetsuo Handa 
Reported-by: syzbot 
Cc: Michal Hocko 
Cc: Vegard Nossum 
Cc: Dmitry Vyukov 
Cc: Jiri Slaby 
Cc: Peter Hurley 
Cc: One Thousand Gnomes 
Cc: Linus Torvalds 
Cc: stable 
Signed-off-by: Greg Kroah-Hartman

tty: Don't call panic() at tty_ldisc_init()

2018-04-23T09:05:52+00:00

syzbot is reporting kernel panic [1] triggered by memory allocation failure
at tty_ldisc_get() from tty_ldisc_init(). But since both tty_ldisc_get()
and caller of tty_ldisc_init() can cleanly handle errors, tty_ldisc_init()
does not need to call panic() when tty_ldisc_get() failed.

[1] https://syzkaller.appspot.com/bug?id=883431818e036ae6a9981156a64b821110f39187

Signed-off-by: Tetsuo Handa 
Reported-by: syzbot 
Cc: Greg Kroah-Hartman 
Cc: Jiri Slaby 
Cc: stable 
Signed-off-by: Greg Kroah-Hartman

tty: Avoid possible error pointer dereference at tty_ldisc_restore().

2018-04-23T09:05:52+00:00

syzbot is reporting crashes [1] triggered by memory allocation failure at
tty_ldisc_get() from tty_ldisc_restore(). While syzbot stops at WARN_ON()
due to panic_on_warn == true, panic_on_warn == false will after all trigger
an OOPS by dereferencing old->ops->num if IS_ERR(old) == true.

We can simplify tty_ldisc_restore() as three calls (old->ops->num, N_TTY,
N_NULL) to tty_ldisc_failto() in addition to avoiding possible error
pointer dereference.

If someone reports kernel panic triggered by forcing all memory allocations
for tty_ldisc_restore() to fail, we can consider adding __GFP_NOFAIL for
tty_ldisc_restore() case.

[1] https://syzkaller.appspot.com/bug?id=6ac359c61e71d22e06db7f8f88243feb11d927e7

Reported-by: syzbot+40b7287c2dc987c48c81@syzkaller.appspotmail.com
Signed-off-by: Tetsuo Handa 
Cc: Greg Kroah-Hartman 
Cc: Jiri Slaby 
Cc: Dmitry Vyukov 
Cc: Johannes Weiner 
Cc: Alan Cox 
Cc: Christoph Hellwig 
Cc: Michal Hocko 
Cc: stable 
Signed-off-by: Greg Kroah-Hartman