6.6-stable review patch. If anyone has any objections, please let me know.
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From: Nikita Zhandarovich n.zhandarovich@fintech.ru
commit 0de7d9cd07a2671fa6089173bccc0b2afe6b93ee upstream.
Syzbot identified an issue [1] that crashes kernel, seemingly due to unexistent callback dev->get_valid_routes(). By all means, this should not occur as said callback must always be set to get_zero_valid_routes() in __comedi_device_postconfig().
As the crash seems to appear exclusively in i386 kernels, at least, judging from [1] reports, the blame lies with compat versions of standard IOCTL handlers. Several of them are modified and do not use comedi_unlocked_ioctl(). While functionality of these ioctls essentially copy their original versions, they do not have required sanity check for device's attached status. This, in turn, leads to a possibility of calling select IOCTLs on a device that has not been properly setup, even via COMEDI_DEVCONFIG.
Doing so on unconfigured devices means that several crucial steps are missed, for instance, specifying dev->get_valid_routes() callback.
Fix this somewhat crudely by ensuring device's attached status before performing any ioctls, improving logic consistency between modern and compat functions.
[1] Syzbot report: BUG: kernel NULL pointer dereference, address: 0000000000000000 ... CR2: ffffffffffffffd6 CR3: 000000006c717000 CR4: 0000000000352ef0 Call Trace: <TASK> get_valid_routes drivers/comedi/comedi_fops.c:1322 [inline] parse_insn+0x78c/0x1970 drivers/comedi/comedi_fops.c:1401 do_insnlist_ioctl+0x272/0x700 drivers/comedi/comedi_fops.c:1594 compat_insnlist drivers/comedi/comedi_fops.c:3208 [inline] comedi_compat_ioctl+0x810/0x990 drivers/comedi/comedi_fops.c:3273 __do_compat_sys_ioctl fs/ioctl.c:695 [inline] __se_compat_sys_ioctl fs/ioctl.c:638 [inline] __ia32_compat_sys_ioctl+0x242/0x370 fs/ioctl.c:638 do_syscall_32_irqs_on arch/x86/entry/syscall_32.c:83 [inline] ...
Reported-by: syzbot+ab8008c24e84adee93ff@syzkaller.appspotmail.com Closes: https://syzkaller.appspot.com/bug?extid=ab8008c24e84adee93ff Fixes: 3fbfd2223a27 ("comedi: get rid of compat_alloc_user_space() mess in COMEDI_CHANINFO compat") Cc: stable stable@kernel.org Reviewed-by: Ian Abbott abbotti@mev.co.uk Signed-off-by: Nikita Zhandarovich n.zhandarovich@fintech.ru Link: https://patch.msgid.link/20251023132234.395794-1-n.zhandarovich@fintech.ru Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- drivers/comedi/comedi_fops.c | 42 ++++++++++++++++++++++++++++++++++++------ 1 file changed, 36 insertions(+), 6 deletions(-)
--- a/drivers/comedi/comedi_fops.c +++ b/drivers/comedi/comedi_fops.c @@ -2971,7 +2971,12 @@ static int compat_chaninfo(struct file * chaninfo.rangelist = compat_ptr(chaninfo32.rangelist);
mutex_lock(&dev->mutex); - err = do_chaninfo_ioctl(dev, &chaninfo); + if (!dev->attached) { + dev_dbg(dev->class_dev, "no driver attached\n"); + err = -ENODEV; + } else { + err = do_chaninfo_ioctl(dev, &chaninfo); + } mutex_unlock(&dev->mutex); return err; } @@ -2992,7 +2997,12 @@ static int compat_rangeinfo(struct file rangeinfo.range_ptr = compat_ptr(rangeinfo32.range_ptr);
mutex_lock(&dev->mutex); - err = do_rangeinfo_ioctl(dev, &rangeinfo); + if (!dev->attached) { + dev_dbg(dev->class_dev, "no driver attached\n"); + err = -ENODEV; + } else { + err = do_rangeinfo_ioctl(dev, &rangeinfo); + } mutex_unlock(&dev->mutex); return err; } @@ -3068,7 +3078,12 @@ static int compat_cmd(struct file *file, return rc;
mutex_lock(&dev->mutex); - rc = do_cmd_ioctl(dev, &cmd, ©, file); + if (!dev->attached) { + dev_dbg(dev->class_dev, "no driver attached\n"); + rc = -ENODEV; + } else { + rc = do_cmd_ioctl(dev, &cmd, ©, file); + } mutex_unlock(&dev->mutex); if (copy) { /* Special case: copy cmd back to user. */ @@ -3093,7 +3108,12 @@ static int compat_cmdtest(struct file *f return rc;
mutex_lock(&dev->mutex); - rc = do_cmdtest_ioctl(dev, &cmd, ©, file); + if (!dev->attached) { + dev_dbg(dev->class_dev, "no driver attached\n"); + rc = -ENODEV; + } else { + rc = do_cmdtest_ioctl(dev, &cmd, ©, file); + } mutex_unlock(&dev->mutex); if (copy) { err = put_compat_cmd(compat_ptr(arg), &cmd); @@ -3153,7 +3173,12 @@ static int compat_insnlist(struct file * }
mutex_lock(&dev->mutex); - rc = do_insnlist_ioctl(dev, insns, insnlist32.n_insns, file); + if (!dev->attached) { + dev_dbg(dev->class_dev, "no driver attached\n"); + rc = -ENODEV; + } else { + rc = do_insnlist_ioctl(dev, insns, insnlist32.n_insns, file); + } mutex_unlock(&dev->mutex); kfree(insns); return rc; @@ -3172,7 +3197,12 @@ static int compat_insn(struct file *file return rc;
mutex_lock(&dev->mutex); - rc = do_insn_ioctl(dev, &insn, file); + if (!dev->attached) { + dev_dbg(dev->class_dev, "no driver attached\n"); + rc = -ENODEV; + } else { + rc = do_insn_ioctl(dev, &insn, file); + } mutex_unlock(&dev->mutex); return rc; }