Re: [PATCH v4] add the option of fortified string.h functions

[Daniel Micay <danielmicay-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>]

On Fri, 2017-06-02 at 14:07 -0700, Andrew Morton wrote:
> On Fri, 26 May 2017 05:54:04 -0400 Daniel Micay <danielmicay-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org
> > wrote:
> 
> > This adds support for compiling with a rough equivalent to the glibc
> > _FORTIFY_SOURCE=1 feature, providing compile-time and runtime buffer
> > overflow checks for string.h functions when the compiler determines
> > the
> > size of the source or destination buffer at compile-time. Unlike
> > glibc,
> > it covers buffer reads in addition to writes.
> 
> Did we find a bug in drivers/infiniband/sw/rxe/rxe_resp.c?
> 
> i386 allmodconfig:
> 
> In file included from ./include/linux/bitmap.h:8:0,
>                  from ./include/linux/cpumask.h:11,
>                  from ./include/linux/mm_types_task.h:13,
>                  from ./include/linux/mm_types.h:4,
>                  from ./include/linux/kmemcheck.h:4,
>                  from ./include/linux/skbuff.h:18,
>                  from drivers/infiniband/sw/rxe/rxe_resp.c:34:
> In function 'memcpy',
>     inlined from 'send_atomic_ack.constprop' at
> drivers/infiniband/sw/rxe/rxe_resp.c:998:2,
>     inlined from 'acknowledge' at
> drivers/infiniband/sw/rxe/rxe_resp.c:1026:3,
>     inlined from 'rxe_responder' at
> drivers/infiniband/sw/rxe/rxe_resp.c:1286:10:
> ./include/linux/string.h:309:4: error: call to '__read_overflow2'
> declared with attribute error: detected read beyond size of object
> passed as 2nd parameter
>     __read_overflow2();
> 
> 
> If so, can you please interpret this for the infiniband developers?

It copies sizeof(skb->cb) bytes with memcpy which is 48 bytes since cb
is a 48 byte char array in `struct sk_buff`. The source buffer is a
`struct rxe_pkt_info`:

struct rxe_pkt_info {
	struct rxe_dev		*rxe;		/* device that owns packet */
	struct rxe_qp		*qp;		/* qp that owns packet */
	struct rxe_send_wqe	*wqe;		/* send wqe */
	u8			*hdr;		/* points to bth */
	u32			mask;		/* useful info about pkt */
	u32			psn;		/* bth psn of packet */
	u16			pkey_index;	/* partition of pkt */
	u16			paylen;		/* length of bth - icrc */
	u8			port_num;	/* port pkt received on */
	u8			opcode;		/* bth opcode of packet */
	u8			offset;		/* bth offset from pkt->hdr */
};

That looks like 32 bytes (1 byte of padding) on 32-bit and 48 bytes on
64-bit (1 byte of padding), so on 32-bit there's a read overflow of 16
bytes from the stack here.
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