mirror of
https://github.com/torvalds/linux.git
synced 2025-12-07 20:06:24 +00:00
1e4b207ffe
The following warning appears when running syzkaller, and this issue also
exists in the mainline code.
------------[ cut here ]------------
list_add double add: new=ffffffffa57eee28, prev=ffffffffa57eee28, next=ffffffffa5e63100.
WARNING: CPU: 0 PID: 1491 at lib/list_debug.c:35 __list_add_valid_or_report+0xf7/0x130
Modules linked in:
CPU: 0 PID: 1491 Comm: syz.1.28 Not tainted 6.6.0+ #3
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.16.0-0-gd239552ce722-prebuilt.qemu.org 04/01/2014
RIP: 0010:__list_add_valid_or_report+0xf7/0x130
RSP: 0018:ff1100010dfb7b78 EFLAGS: 00010282
RAX: 0000000000000000 RBX: ffffffffa57eee18 RCX: ffffffff97fc9817
RDX: 0000000000040000 RSI: ffa0000002383000 RDI: 0000000000000001
RBP: ffffffffa57eee28 R08: 0000000000000001 R09: ffe21c0021bf6f2c
R10: 0000000000000001 R11: 6464615f7473696c R12: ffffffffa5e63100
R13: ffffffffa57eee28 R14: ffffffffa57eee28 R15: ff1100010dfb7d48
FS: 00007fb14398b640(0000) GS:ff11000119600000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000000000000000 CR3: 000000010d096005 CR4: 0000000000773ef0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
PKRU: 80000000
Call Trace:
<TASK>
input_register_handler+0xb3/0x210
mac_hid_start_emulation+0x1c5/0x290
mac_hid_toggle_emumouse+0x20a/0x240
proc_sys_call_handler+0x4c2/0x6e0
new_sync_write+0x1b1/0x2d0
vfs_write+0x709/0x950
ksys_write+0x12a/0x250
do_syscall_64+0x5a/0x110
entry_SYSCALL_64_after_hwframe+0x78/0xe2
The WARNING occurs when two processes concurrently write to the mac-hid
emulation sysctl, causing a race condition in mac_hid_toggle_emumouse().
Both processes read old_val=0, then both try to register the input handler,
leading to a double list_add of the same handler.
CPU0 CPU1
------------------------- -------------------------
vfs_write() //write 1 vfs_write() //write 1
proc_sys_write() proc_sys_write()
mac_hid_toggle_emumouse() mac_hid_toggle_emumouse()
old_val = *valp // old_val=0
old_val = *valp // old_val=0
mutex_lock_killable()
proc_dointvec() // *valp=1
mac_hid_start_emulation()
input_register_handler()
mutex_unlock()
mutex_lock_killable()
proc_dointvec()
mac_hid_start_emulation()
input_register_handler() //Trigger Warning
mutex_unlock()
Fix this by moving the old_val read inside the mutex lock region.
Fixes: 99b089c3c3 ("Input: Mac button emulation - implement as an input filter")
Signed-off-by: Long Li <leo.lilong@huawei.com>
Signed-off-by: Madhavan Srinivasan <maddy@linux.ibm.com>
Link: https://patch.msgid.link/20250819091035.2263329-1-leo.lilong@huaweicloud.com
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 reStructuredText 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.