[PATCH] s390: iucv: Avoid field over-reading memcpy()

[PATCH] s390: iucv: Avoid field over-reading memcpy()

[Kees Cook]

In preparation for FORTIFY_SOURCE performing compile-time and run-time
field bounds checking for memcpy(), memmove(), and memset(), avoid
intentionally reading across neighboring array fields.

Add a wrapping struct to serve as the memcpy() source so the compiler
can perform appropriate bounds checking, avoiding this future warning:

In function '__fortify_memcpy',
    inlined from 'iucv_message_pending' at net/iucv/iucv.c:1663:4:
./include/linux/fortify-string.h:246:4: error: call to '__read_overflow2_field' declared with attribute error: detected read beyond size of field (2nd parameter)

Signed-off-by: Kees Cook <keescook@chromium.org>
---
 net/iucv/iucv.c | 22 ++++++++++++----------
 1 file changed, 12 insertions(+), 10 deletions(-)

diff --git a/net/iucv/iucv.c b/net/iucv/iucv.c
index 349c6ac3313f..e6795d5a546a 100644
--- a/net/iucv/iucv.c
+++ b/net/iucv/iucv.c
@@ -1635,14 +1635,16 @@ struct iucv_message_pending {
 	u8  iptype;
 	u32 ipmsgid;
 	u32 iptrgcls;
-	union {
-		u32 iprmmsg1_u32;
-		u8  iprmmsg1[4];
-	} ln1msg1;
-	union {
-		u32 ipbfln1f;
-		u8  iprmmsg2[4];
-	} ln1msg2;
+	struct {
+		union {
+			u32 iprmmsg1_u32;
+			u8  iprmmsg1[4];
+		} ln1msg1;
+		union {
+			u32 ipbfln1f;
+			u8  iprmmsg2[4];
+		} ln1msg2;
+	} rmmsg;
 	u32 res1[3];
 	u32 ipbfln2f;
 	u8  ippollfg;
@@ -1660,10 +1662,10 @@ static void iucv_message_pending(struct iucv_irq_data *data)
 		msg.id = imp->ipmsgid;
 		msg.class = imp->iptrgcls;
 		if (imp->ipflags1 & IUCV_IPRMDATA) {
-			memcpy(msg.rmmsg, imp->ln1msg1.iprmmsg1, 8);
+			memcpy(msg.rmmsg, &imp->rmmsg, 8);
 			msg.length = 8;
 		} else
-			msg.length = imp->ln1msg2.ipbfln1f;
+			msg.length = imp->rmmsg.ln1msg2.ipbfln1f;
 		msg.reply_size = imp->ipbfln2f;
 		path->handler->message_pending(path, &msg);
 	}
-- 
2.25.1

Re: [PATCH] s390: iucv: Avoid field over-reading memcpy()

[Heiko Carstens]

On Wed, Jun 16, 2021 at 01:19:42PM -0700, Kees Cook wrote:
> In preparation for FORTIFY_SOURCE performing compile-time and run-time
> field bounds checking for memcpy(), memmove(), and memset(), avoid
> intentionally reading across neighboring array fields.
> 
> Add a wrapping struct to serve as the memcpy() source so the compiler
> can perform appropriate bounds checking, avoiding this future warning:
> 
> In function '__fortify_memcpy',
>     inlined from 'iucv_message_pending' at net/iucv/iucv.c:1663:4:
> ./include/linux/fortify-string.h:246:4: error: call to '__read_overflow2_field' declared with attribute error: detected read beyond size of field (2nd parameter)
> 
> Signed-off-by: Kees Cook <keescook@chromium.org>
> ---
>  net/iucv/iucv.c | 22 ++++++++++++----------
>  1 file changed, 12 insertions(+), 10 deletions(-)

This one is for Julian Wiedmann and Karsten Graul.

Re: [PATCH] s390: iucv: Avoid field over-reading memcpy()

[Karsten Graul]

On 16/06/2021 22:19, Kees Cook wrote:
> In preparation for FORTIFY_SOURCE performing compile-time and run-time
> field bounds checking for memcpy(), memmove(), and memset(), avoid
> intentionally reading across neighboring array fields.
> 
> Add a wrapping struct to serve as the memcpy() source so the compiler
> can perform appropriate bounds checking, avoiding this future warning:
> 
> In function '__fortify_memcpy',
>     inlined from 'iucv_message_pending' at net/iucv/iucv.c:1663:4:
> ./include/linux/fortify-string.h:246:4: error: call to '__read_overflow2_field' declared with attribute error: detected read beyond size of field (2nd parameter)
> 
> Signed-off-by: Kees Cook <keescook@chromium.org>

Looks good, thanks for taking care of that change.

Acked-by: Karsten Graul <kgraul@linux.ibm.com>

> ---
>  net/iucv/iucv.c | 22 ++++++++++++----------
>  1 file changed, 12 insertions(+), 10 deletions(-)
> 
> diff --git a/net/iucv/iucv.c b/net/iucv/iucv.c
> index 349c6ac3313f..e6795d5a546a 100644
> --- a/net/iucv/iucv.c
> +++ b/net/iucv/iucv.c
> @@ -1635,14 +1635,16 @@ struct iucv_message_pending {
>  	u8  iptype;
>  	u32 ipmsgid;
>  	u32 iptrgcls;
> -	union {
> -		u32 iprmmsg1_u32;
> -		u8  iprmmsg1[4];
> -	} ln1msg1;
> -	union {
> -		u32 ipbfln1f;
> -		u8  iprmmsg2[4];
> -	} ln1msg2;
> +	struct {
> +		union {
> +			u32 iprmmsg1_u32;
> +			u8  iprmmsg1[4];
> +		} ln1msg1;
> +		union {
> +			u32 ipbfln1f;
> +			u8  iprmmsg2[4];
> +		} ln1msg2;
> +	} rmmsg;
>  	u32 res1[3];
>  	u32 ipbfln2f;
>  	u8  ippollfg;
> @@ -1660,10 +1662,10 @@ static void iucv_message_pending(struct iucv_irq_data *data)
>  		msg.id = imp->ipmsgid;
>  		msg.class = imp->iptrgcls;
>  		if (imp->ipflags1 & IUCV_IPRMDATA) {
> -			memcpy(msg.rmmsg, imp->ln1msg1.iprmmsg1, 8);
> +			memcpy(msg.rmmsg, &imp->rmmsg, 8);
>  			msg.length = 8;
>  		} else
> -			msg.length = imp->ln1msg2.ipbfln1f;
> +			msg.length = imp->rmmsg.ln1msg2.ipbfln1f;
>  		msg.reply_size = imp->ipbfln2f;
>  		path->handler->message_pending(path, &msg);
>  	}
> 

-- 
Karsten

(I'm a dude)