On 18.04.2018 10:07, Uwe Kleine-König wrote:
> Hello,
Hello Uwe,
Thanks for your reply.
> On Wed, Apr 18, 2018 at 03:16:45AM +0300, Alexander Popov wrote:
>> Currently i2cdev_ioctl_rdwr() doesn't check i2c_msg len against zero
>> before calling memdup_user(). If this len is zero memdup_user() returns
>> ZERO_SIZE_PTR, which is later considered as valid since
>> IS_ERR(ZERO_SIZE_PTR) is false. That causes ZERO_SIZE_PTR deref oops.
>
> You're saying that
>
> memdup_user(ptr, 0)
>
> reads from *ptr? I'd say this is a bug in memdup_user, not its user.
No, I don't say that.
memdup_user(ptr, 0) returns ZERO_SIZE_PTR, which is later considered as valid
since IS_ERR(ZERO_SIZE_PTR) is false:
msgs[i].buf = memdup_user(data_ptrs[i], msgs[i].len);
if (IS_ERR(msgs[i].buf)) {
res = PTR_ERR(msgs[i].buf);
break;
}
That causes ZERO_SIZE_PTR deref oops after that:
root@syzkaller:~# ./repro
[ 22.015442] kasan: CONFIG_KASAN_INLINE enabled
[ 22.066965] kasan: GPF could be caused by NULL-ptr deref or user memory access
[ 22.068624] general protection fault: 0000 [#1] SMP KASAN
[ 22.069705] Dumping ftrace buffer:
[ 22.070399] (ftrace buffer empty)
[ 22.071033] Modules linked in:
[ 22.071562] CPU: 0 PID: 3899 Comm: repro.exe Not tainted 4.17.0-rc1 #2
[ 22.072632] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS
Ubuntu-1.8.2-1ubuntu1 04/01/2014
[ 22.074219] RIP: 0010:i2cdev_ioctl_rdwr+0x12b/0x7b0
[ 22.075023] RSP: 0018:ffff880061f3fa68 EFLAGS: 00010346
[ 22.075877] RAX: 0000000000000002 RBX: 0000000000000000 RCX: 0000000000000000
[ 22.076973] RDX: 0000000000000000 RSI: 0000000020000000 RDI: ffff88006a2e9542
[ 22.078086] RBP: ffff880061f3fac0 R08: 0000000000000000 R09: ffff880060b44780
[ 22.079166] R10: 1ffff1000c3e7f1d R11: 0000000000000000 R12: dffffc0000000000
[ 22.080251] R13: ffff88006a2e9540 R14: 0000000000000010 R15: 0000000000000001
[ 22.081339] FS: 00000000020bc880(0000) GS:ffff88006ba00000(0000)
knlGS:0000000000000000
[ 22.082615] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[ 22.083526] CR2: 00000000200002c3 CR3: 000000006724a000 CR4: 00000000000006f0
[ 22.084631] Call Trace:
[ 22.085501] ? i2cdev_ioctl_rdwr+0xf/0x7b0
[ 22.086865] i2cdev_ioctl+0x4ec/0x940
[ 22.088677] ? kasan_check_read+0x11/0x20
[ 22.090555] ? i2cdev_ioctl_smbus+0x6a0/0x6a0
[ 22.091862] ? do_raw_spin_trylock+0x1e0/0x1e0
[ 22.092428] ? kasan_check_write+0x14/0x20
[ 22.092946] ? trace_hardirqs_off+0xd/0x10
[ 22.093451] ? _raw_spin_unlock_irqrestore+0xa6/0xe0
[ 22.094013] ? debug_check_no_obj_freed+0x341/0x7eb
[ 22.094547] ? i2cdev_ioctl_smbus+0x6a0/0x6a0
[ 22.095086] do_vfs_ioctl+0x1cd/0x17b0
[ 22.095482] ? kasan_check_read+0x11/0x20
[ 22.095978] ? rcu_is_watching+0x7b/0x150
[ 22.096428] ? ioctl_preallocate+0x350/0x350
[ 22.096908] ? __fget_light+0x2fc/0x4c0
[ 22.097351] ? fget_raw+0x20/0x20
[ 22.097721] ? kmem_cache_free+0x31c/0x450
[ 22.098164] ? putname+0xfa/0x150
[ 22.098511] ? do_sys_open+0x31c/0x710
[ 22.099792] ? security_file_ioctl+0x8c/0xc0
[ 22.102080] ksys_ioctl+0x94/0xb0
[ 22.103204] __x64_sys_ioctl+0x7c/0xd0
[ 22.103643] do_syscall_64+0x193/0x920
[ 22.104186] ? trace_event_raw_event_sys_exit+0x2e0/0x2e0
[ 22.105061] ? syscall_return_slowpath+0x6a0/0x6a0
[ 22.106717] ? syscall_return_slowpath+0x2de/0x6a0
[ 22.108183] ? entry_SYSCALL_64_after_hwframe+0x59/0xbe
[ 22.109597] ? trace_hardirqs_off_thunk+0x1a/0x1c
[ 22.110167] entry_SYSCALL_64_after_hwframe+0x49/0xbe
[ 22.110735] RIP: 0033:0x44df89
[ 22.111077] RSP: 002b:00007fff7fb01ca8 EFLAGS: 00000213 ORIG_RAX:
0000000000000010
[ 22.111932] RAX: ffffffffffffffda RBX: 0000000000400418 RCX: 000000000044df89
[ 22.112958] RDX: 0000000020000080 RSI: 0000000000000707 RDI: 0000000000000003
[ 22.114078] RBP: 00007fff7fb01cc0 R08: 0000000000000000 R09: 0000000000401af0
[ 22.115784] R10: 000000000000ffff R11: 0000000000000213 R12: 0000000000401b90
[ 22.116870] R13: 0000000000000000 R14: 00000000006bd018 R15: 0000000000000000
[ 22.117953] Code: 00 e8 7a 53 bd fb 41 83 e7 01 0f 84 e8 03 00 00 e8 6b 53 bd
fb 4d 85 f6 0f 84 12 06 00 00 4c 89 f0 4c 89 f1 48 c1 e8 03 83 e1 07 <42> 0f b6
04 20 38 c8 7f 08 84 c0 0f 85 e7 05 00 00 45 0f b6 36
[ 22.120532] RIP: i2cdev_ioctl_rdwr+0x12b/0x7b0 RSP: ffff880061f3fa68
[ 22.121290] ---[ end trace b365c176b1d95614 ]---
> If however the problem only happens later in
>
> if (msgs[i].flags & I2C_M_RECV_LEN) {
> if (!(msgs[i].flags & I2C_M_RD) || msgs[i].buf[0] < 1 || ...)
Yes, that's true. I think I should make the commit message more verbose. I'll
come with v2.
> Your commit log is wrong (and I think the patch, too).
I believe this bug is not a memdup_user() issue. There is a nice selection from
LKML discussions about ZERO_SIZE_PTR, which convinces me:
http://yarchive.net/comp/linux/malloc_0.html
Best regards,
Alexander
