6.18-stable review patch. If anyone has any objections, please let me know.
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From: Nikita Zhandarovich n.zhandarovich@fintech.ru
commit f24c6e3a39fa355dabfb684c9ca82db579534e72 upstream.
Syzbot identified an issue [1] in multiq3_attach() that induces a task timeout due to open() or COMEDI_DEVCONFIG ioctl operations, specifically, in the case of multiq3 driver.
This problem arose when syzkaller managed to craft weird configuration options used to specify the number of channels in encoder subdevice. If a particularly great number is passed to s->n_chan in multiq3_attach() via it->options[2], then multiple calls to multiq3_encoder_reset() at the end of driver-specific attach() method will be running for minutes, thus blocking tasks and affected devices as well.
While this issue is most likely not too dangerous for real-life devices, it still makes sense to sanitize configuration inputs. Enable a sensible limit on the number of encoder chips (4 chips max, each with 2 channels) to stop this behaviour from manifesting.
[1] Syzbot crash: INFO: task syz.2.19:6067 blocked for more than 143 seconds. ... Call Trace: <TASK> context_switch kernel/sched/core.c:5254 [inline] __schedule+0x17c4/0x4d60 kernel/sched/core.c:6862 __schedule_loop kernel/sched/core.c:6944 [inline] schedule+0x165/0x360 kernel/sched/core.c:6959 schedule_preempt_disabled+0x13/0x30 kernel/sched/core.c:7016 __mutex_lock_common kernel/locking/mutex.c:676 [inline] __mutex_lock+0x7e6/0x1350 kernel/locking/mutex.c:760 comedi_open+0xc0/0x590 drivers/comedi/comedi_fops.c:2868 chrdev_open+0x4cc/0x5e0 fs/char_dev.c:414 do_dentry_open+0x953/0x13f0 fs/open.c:965 vfs_open+0x3b/0x340 fs/open.c:1097 ...
Reported-by: syzbot+7811bb68a317954a0347@syzkaller.appspotmail.com Closes: https://syzkaller.appspot.com/bug?extid=7811bb68a317954a0347 Fixes: 77e01cdbad51 ("Staging: comedi: add multiq3 driver") Cc: stable stable@kernel.org Signed-off-by: Nikita Zhandarovich n.zhandarovich@fintech.ru Reviewed-by: Ian Abbott abbotti@mev.co.uk Link: https://patch.msgid.link/20251023132205.395753-1-n.zhandarovich@fintech.ru Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- drivers/comedi/drivers/multiq3.c | 9 +++++++++ 1 file changed, 9 insertions(+)
--- a/drivers/comedi/drivers/multiq3.c +++ b/drivers/comedi/drivers/multiq3.c @@ -67,6 +67,11 @@ #define MULTIQ3_TRSFRCNTR_OL 0x10 /* xfer CNTR to OL (x and y) */ #define MULTIQ3_EFLAG_RESET 0x06 /* reset E bit of flag reg */
+/* + * Limit on the number of optional encoder channels + */ +#define MULTIQ3_MAX_ENC_CHANS 8 + static void multiq3_set_ctrl(struct comedi_device *dev, unsigned int bits) { /* @@ -312,6 +317,10 @@ static int multiq3_attach(struct comedi_ s->insn_read = multiq3_encoder_insn_read; s->insn_config = multiq3_encoder_insn_config;
+ /* sanity check for number of encoder channels */ + if (s->n_chan > MULTIQ3_MAX_ENC_CHANS) + s->n_chan = MULTIQ3_MAX_ENC_CHANS; + for (i = 0; i < s->n_chan; i++) multiq3_encoder_reset(dev, i);