| From: Jiri Slaby <jslaby@suse.cz> |
| Date: Fri, 28 Feb 2020 12:54:06 +0100 |
| Subject: vt: selection, push sel_lock up |
| |
| commit e8c75a30a23c6ba63f4ef6895cbf41fd42f21aa2 upstream. |
| |
| sel_lock cannot nest in the console lock. Thanks to syzkaller, the |
| kernel states firmly: |
| |
| > WARNING: possible circular locking dependency detected |
| > 5.6.0-rc3-syzkaller #0 Not tainted |
| > ------------------------------------------------------ |
| > syz-executor.4/20336 is trying to acquire lock: |
| > ffff8880a2e952a0 (&tty->termios_rwsem){++++}, at: tty_unthrottle+0x22/0x100 drivers/tty/tty_ioctl.c:136 |
| > |
| > but task is already holding lock: |
| > ffffffff89462e70 (sel_lock){+.+.}, at: paste_selection+0x118/0x470 drivers/tty/vt/selection.c:374 |
| > |
| > which lock already depends on the new lock. |
| > |
| > the existing dependency chain (in reverse order) is: |
| > |
| > -> #2 (sel_lock){+.+.}: |
| > mutex_lock_nested+0x1b/0x30 kernel/locking/mutex.c:1118 |
| > set_selection_kernel+0x3b8/0x18a0 drivers/tty/vt/selection.c:217 |
| > set_selection_user+0x63/0x80 drivers/tty/vt/selection.c:181 |
| > tioclinux+0x103/0x530 drivers/tty/vt/vt.c:3050 |
| > vt_ioctl+0x3f1/0x3a30 drivers/tty/vt/vt_ioctl.c:364 |
| |
| This is ioctl(TIOCL_SETSEL). |
| Locks held on the path: console_lock -> sel_lock |
| |
| > -> #1 (console_lock){+.+.}: |
| > console_lock+0x46/0x70 kernel/printk/printk.c:2289 |
| > con_flush_chars+0x50/0x650 drivers/tty/vt/vt.c:3223 |
| > n_tty_write+0xeae/0x1200 drivers/tty/n_tty.c:2350 |
| > do_tty_write drivers/tty/tty_io.c:962 [inline] |
| > tty_write+0x5a1/0x950 drivers/tty/tty_io.c:1046 |
| |
| This is write(). |
| Locks held on the path: termios_rwsem -> console_lock |
| |
| > -> #0 (&tty->termios_rwsem){++++}: |
| > down_write+0x57/0x140 kernel/locking/rwsem.c:1534 |
| > tty_unthrottle+0x22/0x100 drivers/tty/tty_ioctl.c:136 |
| > mkiss_receive_buf+0x12aa/0x1340 drivers/net/hamradio/mkiss.c:902 |
| > tty_ldisc_receive_buf+0x12f/0x170 drivers/tty/tty_buffer.c:465 |
| > paste_selection+0x346/0x470 drivers/tty/vt/selection.c:389 |
| > tioclinux+0x121/0x530 drivers/tty/vt/vt.c:3055 |
| > vt_ioctl+0x3f1/0x3a30 drivers/tty/vt/vt_ioctl.c:364 |
| |
| This is ioctl(TIOCL_PASTESEL). |
| Locks held on the path: sel_lock -> termios_rwsem |
| |
| > other info that might help us debug this: |
| > |
| > Chain exists of: |
| > &tty->termios_rwsem --> console_lock --> sel_lock |
| |
| Clearly. From the above, we have: |
| console_lock -> sel_lock |
| sel_lock -> termios_rwsem |
| termios_rwsem -> console_lock |
| |
| Fix this by reversing the console_lock -> sel_lock dependency in |
| ioctl(TIOCL_SETSEL). First, lock sel_lock, then console_lock. |
| |
| Signed-off-by: Jiri Slaby <jslaby@suse.cz> |
| Reported-by: syzbot+26183d9746e62da329b8@syzkaller.appspotmail.com |
| Fixes: 07e6124a1a46 ("vt: selection, close sel_buffer race") |
| Link: https://lore.kernel.org/r/20200228115406.5735-2-jslaby@suse.cz |
| Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> |
| Signed-off-by: Ben Hutchings <ben@decadent.org.uk> |
| --- |
| drivers/tty/vt/selection.c | 16 +++++++--------- |
| 1 file changed, 7 insertions(+), 9 deletions(-) |
| |
| --- a/drivers/tty/vt/selection.c |
| +++ b/drivers/tty/vt/selection.c |
| @@ -205,7 +205,6 @@ static int __set_selection(const struct |
| pe = tmp; |
| } |
| |
| - mutex_lock(&sel_lock); |
| if (sel_cons != vc_cons[fg_console].d) { |
| clear_selection(); |
| sel_cons = vc_cons[fg_console].d; |
| @@ -251,10 +250,9 @@ static int __set_selection(const struct |
| break; |
| case TIOCL_SELPOINTER: |
| highlight_pointer(pe); |
| - goto unlock; |
| + return 0; |
| default: |
| - ret = -EINVAL; |
| - goto unlock; |
| + return -EINVAL; |
| } |
| |
| /* remove the pointer */ |
| @@ -276,7 +274,7 @@ static int __set_selection(const struct |
| else if (new_sel_start == sel_start) |
| { |
| if (new_sel_end == sel_end) /* no action required */ |
| - goto unlock; |
| + return 0; |
| else if (new_sel_end > sel_end) /* extend to right */ |
| highlight(sel_end + 2, new_sel_end); |
| else /* contract from right */ |
| @@ -303,8 +301,7 @@ static int __set_selection(const struct |
| if (!bp) { |
| printk(KERN_WARNING "selection: kmalloc() failed\n"); |
| clear_selection(); |
| - ret = -ENOMEM; |
| - goto unlock; |
| + return -ENOMEM; |
| } |
| kfree(sel_buffer); |
| sel_buffer = bp; |
| @@ -329,8 +326,7 @@ static int __set_selection(const struct |
| } |
| } |
| sel_buffer_lth = bp - sel_buffer; |
| -unlock: |
| - mutex_unlock(&sel_lock); |
| + |
| return ret; |
| } |
| |
| @@ -338,9 +334,11 @@ int set_selection(const struct tiocl_sel |
| { |
| int ret; |
| |
| + mutex_lock(&sel_lock); |
| console_lock(); |
| ret = __set_selection(v, tty); |
| console_unlock(); |
| + mutex_unlock(&sel_lock); |
| |
| return ret; |
| } |