0a360e8b65
Add the error path for registering tty devices and roll back in case of error in bid to avoid the UAF like the below one reported. Plus syzbot reported general protection fault in cdev_del() on Sep 24, 2020 and both cases are down to the kobject_put() in tty_cdev_add(). ------------[ cut here ]------------ refcount_t: underflow; use-after-free. WARNING: CPU: 1 PID: 8923 at lib/refcount.c:28 refcount_warn_saturate+0x1cf/0x210 -origin/lib/refcount.c:28 Modules linked in: CPU: 1 PID: 8923 Comm: executor Not tainted 5.12.0-rc5+ #8 Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.13.0-1ubuntu1.1 04/01/2014 RIP: 0010:refcount_warn_saturate+0x1cf/0x210 -origin/lib/refcount.c:28 Code: 4f ff ff ff e8 32 fa b5 fe 48 c7 c7 3d f8 f6 86 e8 d6 ab c6 fe c6 05 7c 34 67 04 01 48 c7 c7 68 f8 6d 86 31 c0 e8 81 2e 9d fe <0f> 0b e9 22 ff ff ff e8 05 fa b5 fe 48 c7 c7 3e f8 f6 86 e8 a9 ab RSP: 0018:ffffc90001633c60 EFLAGS: 00010246 RAX: 15d08b2e34b77800 RBX: 0000000000000003 RCX: ffff88804c056c80 RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000000 RBP: 0000000000000003 R08: ffffffff813767aa R09: 0001ffffffffffff R10: 0001ffffffffffff R11: ffff88804c056c80 R12: ffff888040b7d000 R13: ffff88804c206938 R14: ffff88804c206900 R15: ffff888041b18488 FS: 00000000022c9940(0000) GS:ffff88807ec00000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 CR2: 00007f9f9b122008 CR3: 0000000044b4b000 CR4: 0000000000750ee0 PKRU: 55555554 Call Trace: __refcount_sub_and_test -origin/./include/linux/refcount.h:283 [inline] __refcount_dec_and_test -origin/./include/linux/refcount.h:315 [inline] refcount_dec_and_test -origin/./include/linux/refcount.h:333 [inline] kref_put -origin/./include/linux/kref.h:64 [inline] kobject_put+0x17b/0x180 -origin/lib/kobject.c:753 cdev_del+0x4b/0x50 -origin/fs/char_dev.c:597 tty_unregister_device+0x99/0xd0 -origin/drivers/tty/tty_io.c:3343 gsmld_detach_gsm -origin/drivers/tty/n_gsm.c:2409 [inline] gsmld_close+0x6c/0x140 -origin/drivers/tty/n_gsm.c:2478 tty_ldisc_close -origin/drivers/tty/tty_ldisc.c:488 [inline] tty_ldisc_kill -origin/drivers/tty/tty_ldisc.c:636 [inline] tty_ldisc_release+0x1b6/0x400 -origin/drivers/tty/tty_ldisc.c:809 tty_release_struct+0x19/0xb0 -origin/drivers/tty/tty_io.c:1714 tty_release+0x9ad/0xa00 -origin/drivers/tty/tty_io.c:1885 __fput+0x260/0x4e0 -origin/fs/file_table.c:280 ____fput+0x11/0x20 -origin/fs/file_table.c:313 task_work_run+0x8e/0x110 -origin/kernel/task_work.c:140 tracehook_notify_resume -origin/./include/linux/tracehook.h:189 [inline] exit_to_user_mode_loop -origin/kernel/entry/common.c:174 [inline] exit_to_user_mode_prepare+0x16b/0x1a0 -origin/kernel/entry/common.c:208 __syscall_exit_to_user_mode_work -origin/kernel/entry/common.c:290 [inline] syscall_exit_to_user_mode+0x20/0x40 -origin/kernel/entry/common.c:301 do_syscall_64+0x45/0x80 -origin/arch/x86/entry/common.c:56 entry_SYSCALL_64_after_hwframe+0x44/0xae Reported-by: syzbot+c49fe6089f295a05e6f8@syzkaller.appspotmail.com Reported-and-tested-by: Hao Sun <sunhao.th@gmail.com> Signed-off-by: Hillf Danton <hdanton@sina.com> Link: https://lore.kernel.org/r/20210412035758.1974-1-hdanton@sina.com Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.