Description

In the Linux kernel, the following vulnerability has been resolved: comedi: check device's attached status in compat ioctls 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] ...

References 8

• git.kernel.org https://git.kernel.org/stable/c/0de7d9cd07a2671fa6089173bccc0b2afe6b93ee
• git.kernel.org https://git.kernel.org/stable/c/4836ba483a22ebd076c8faaf8293a7295fad4142
• git.kernel.org https://git.kernel.org/stable/c/573b07d2e3d473ee7eb625ef87519922cf01168d
• git.kernel.org https://git.kernel.org/stable/c/7141915bf0c41cb57d83cdbaf695b8c731b16b71
• git.kernel.org https://git.kernel.org/stable/c/aac80e912de306815297a3b74f0426873ffa7dc3
• git.kernel.org https://git.kernel.org/stable/c/b975f91de5f8f63cf490f0393775cc795f8b0557
• git.kernel.org https://git.kernel.org/stable/c/f13895c03620933a58907e3250016f087e39b78c
• git.kernel.org https://git.kernel.org/stable/c/f6e629dfe6f590091c662a87c9fcf118b1c1c7dc

Remediation