Re: [PATCH] To fix the below failure of handling page fault caused by the invalid input from user.

[Manfred Spraul]

Hi Dongyang,

On 1/26/22 03:42, Andrew Morton wrote:
> On Tue, 18 Jan 2022 17:19:52 +0800 Dongyang Wang <dongyang.wang@xxxxxxxxxxxxx> wrote:
>
> > [786058.308965] Unable to handle kernel paging request at virtual address 01000004
> > [786058.316286] pgd = 38a99693
> > [786058.319080] [01000004] *pgd=07800003, *pmd=00000000
> > [786058.324056] Internal error: Oops: 206 [#1] PREEMPT SMP ARM
> > [786058.324100] CPU:  PID: Comm:  Tainted: G         C
> > [786058.324102] Hardware name:
> > [786058.324114] PC is at __copy_to_user_std+0x4c/0x3c4
> > [786058.324120] LR is at store_msg+0xc0/0xe8
> > [786058.324124] pc : [<c0c0587c>]    lr : [<c0871d04>]    psr: 20010013
> > [786058.324126] sp : c3503ec4  ip : 00000000  fp : b4c9a660
> > [786058.324129] r10: c4228dc0  r9 : c3502000  r8 : 00000ffc
> > [786058.324132] r7 : 01000000  r6 : 546d3f8b  r5 : b4911690  r4 : 00000ffc
> > [786058.324134] r3 : 00000000  r2 : 00000f7c  r1 : 01000004  r0 : b4911690
> > [786058.324139] Flags: nzCv  IRQs on  FIQs on  Mode SVC_32  ISA ARM  Segment user
> > [786058.324142] Control: 30c5387d  Table: 0edc2040  DAC: 55555555
> > [786058.324145] Process  (pid: , stack limit = 0x25018bdf)

Why is process and pid: empty? Is this some kind of kernel process calling?


> > [786058.324148] Stack: (0xc3503ec4 to 0xc3504000)
> > [786058.324153] 3ec0:          b4911690 546d3f8b 01000000 00000ffc b4911690 00000ffc 00000000
> > [786058.324157] 3ee0: 00000ffc c0871d04 546d4f73 c3407801 c3503f28 c3407800 00000000 b49106a8
> > [786058.324161] 3f00: c4228dc0 c087abd4 00000002 b49106a8 617b9d03 00000000 00000000 c121d508
> > [786058.324165] 3f20: 00000000 bf06a1a8 d1b634cc 16b26e77 c5af5280 00000100 00000200 db806540
> > [786058.324170] 3f40: 00000001 c121d508 00000008 0000005c 00000000 00010008 b49106a8 c0601208
> > [786058.324173] 3f60: c3502000 00000040 b4c9a660 c087b474 c3503f78 c121d508 617b9d03 00000000
> > [786058.324177] 3f80: 2303d6cc 00000115 c0601208 c121d508 b4c9a660 b4c9a660 00000001 b49106a8
> > [786058.324181] 3fa0: 00000115 c06011dc b4c9a660 00000001 0000005c b49106a8 00010008 00000000
> > [786058.324185] 3fc0: b4c9a660 00000001 b49106a8 00000115 00000000 b4c9b400 00000000 b4c9a660
> > [786058.324189] 3fe0: 00000115 b4c9a650 b6b253bd b6b254b6 800d0030 0000005c 00000000 00000000
> > [786058.324201] [<c0c0587c>] (__copy_to_user_std) from [<c0871d04>] (store_msg+0xc0/0xe8)
> > [786058.324211] [<c0871d04>] (store_msg) from [<c087abd4>] (do_mq_timedreceive+0x29c/0x484)
> > [786058.324218] [<c087abd4>] (do_mq_timedreceive) from [<c087b474>] (sys_mq_timedreceive+0x88/0xbc)
> > [786058.324226] [<c087b474>] (sys_mq_timedreceive) from [<c06011dc>] (__sys_trace_return+0x0/0x10)
> > [786058.324229] Exception stack(0xc3503fa8 to 0xc3503ff0)
> > [786058.324233] 3fa0:                   b4c9a660 00000001 0000005c b49106a8 00010008 00000000
> > [786058.324236] 3fc0: b4c9a660 00000001 b49106a8 00000115 00000000 b4c9b400 00000000 b4c9a660
> > [786058.324239] 3fe0: 00000115 b4c9a650 b6b253bd b6b254b6
> > [786058.324247] Code: ba000002 f5d1f03c f5d1f05c f5d1f07c (e8b151f8)
> > [786058.601808] ---[ end trace 0000000000000002 ]---
> >
> > ...
> Please describe the circumstances under which this occurs.
>
> Please also describe how your proposed patch fixes this.
>
> > --- a/ipc/mqueue.c
> > +++ b/ipc/mqueue.c
> > @@ -1211,6 +1211,12 @@ static int do_mq_timedreceive(mqd_t mqdes, char __user *u_msg_ptr,
> >   		goto out_fput;
> >   	}
> >   
> > +	/* checks if buffer is invalid */
> > +	if ((unsigned long) u_msg_ptr < PAGE_SIZE) {
> > +		ret = -EINVAL;
> > +		goto out_fput;
> > +	}
> > +

I do not think that this will solve the problem: u_msg_ptr is user 
controlled.

If < PAGE_SIZE causes issues, then 2^32-1, or PAGE_SIZE+1 will cause 
issues as well.

What is the kernel version where you have observed the issue?

> >   	/*
> >   	 * msg_insert really wants us to have a valid, spare node struct so
> >   	 * it doesn't have to kmalloc a GFP_ATOMIC allocation, but it will
> > @@ -1262,6 +1268,10 @@ static int do_mq_timedreceive(mqd_t mqdes, char __user *u_msg_ptr,
> >   			store_msg(u_msg_ptr, msg_ptr, msg_ptr->m_ts)) {
> >   			ret = -EFAULT;
> >   		}
> > +
> > +		if (msg_len < ret)
> > +			ret = -EMSGSIZE;
> > +

Why this change?

EMSGSIZE means right now: wrong parameters, no message removed from the 
queue.

But: in the line you modify, a message was already removed from the 
queue. Thus I would not consider EMSGSIZE as appropriate.

> >   		free_msg(msg_ptr);
> >   	}
> >   out_fput:
> > --
> > 2.26.1