[PATCH] ip_options_compile: properly handle unaligned pointer

[PATCH] ip_options_compile: properly handle unaligned pointer

[Chris Metcalf]

The current code takes an unaligned pointer and does htonl() on it to
make it big-endian, then does a memcpy().  The problem is that the
compiler decides that since the pointer is to a __be32, it is legal
to optimize the copy into a processor word store.  However, on an
architecture that does not handled unaligned writes in kernel space,
this produces an unaligned exception fault.

The solution is to track the pointer as a "char *" (which removes a bunch
of unpleasant casts in any case), and then just use put_unaligned_be32()
to write the value to memory.

Signed-off-by: Chris Metcalf <cmetcalf@tilera.com>
---
 net/ipv4/ip_options.c |   15 ++++++++-------
 1 files changed, 8 insertions(+), 7 deletions(-)

diff --git a/net/ipv4/ip_options.c b/net/ipv4/ip_options.c
index 2391b24..a12d33f 100644
--- a/net/ipv4/ip_options.c
+++ b/net/ipv4/ip_options.c
@@ -14,6 +14,7 @@
 #include <linux/slab.h>
 #include <linux/types.h>
 #include <asm/uaccess.h>
+#include <asm/unaligned.h>
 #include <linux/skbuff.h>
 #include <linux/ip.h>
 #include <linux/icmp.h>
@@ -352,7 +353,7 @@ int ip_options_compile(struct net *net,
 				goto error;
 			}
 			if (optptr[2] <= optlen) {
-				__be32 *timeptr = NULL;
+				unsigned char *timeptr = NULL;
 				if (optptr[2]+3 > optptr[1]) {
 					pp_ptr = optptr + 2;
 					goto error;
@@ -361,7 +362,7 @@ int ip_options_compile(struct net *net,
 				      case IPOPT_TS_TSONLY:
 					opt->ts = optptr - iph;
 					if (skb)
-						timeptr = (__be32*)&optptr[optptr[2]-1];
+						timeptr = &optptr[optptr[2]-1];
 					opt->ts_needtime = 1;
 					optptr[2] += 4;
 					break;
@@ -373,7 +374,7 @@ int ip_options_compile(struct net *net,
 					opt->ts = optptr - iph;
 					if (rt)  {
 						memcpy(&optptr[optptr[2]-1], &rt->rt_spec_dst, 4);
-						timeptr = (__be32*)&optptr[optptr[2]+3];
+						timeptr = &optptr[optptr[2]+3];
 					}
 					opt->ts_needaddr = 1;
 					opt->ts_needtime = 1;
@@ -391,7 +392,7 @@ int ip_options_compile(struct net *net,
 						if (inet_addr_type(net, addr) == RTN_UNICAST)
 							break;
 						if (skb)
-							timeptr = (__be32*)&optptr[optptr[2]+3];
+							timeptr = &optptr[optptr[2]+3];
 					}
 					opt->ts_needtime = 1;
 					optptr[2] += 8;
@@ -405,10 +406,10 @@ int ip_options_compile(struct net *net,
 				}
 				if (timeptr) {
 					struct timespec tv;
-					__be32  midtime;
+					u32  midtime;
 					getnstimeofday(&tv);
-					midtime = htonl((tv.tv_sec % 86400) * MSEC_PER_SEC + tv.tv_nsec / NSEC_PER_MSEC);
-					memcpy(timeptr, &midtime, sizeof(__be32));
+					midtime = (tv.tv_sec % 86400) * MSEC_PER_SEC + tv.tv_nsec / NSEC_PER_MSEC;
+					put_unaligned_be32(midtime, timeptr);
 					opt->is_changed = 1;
 				}
 			} else {
-- 
1.6.5.2

Re: [PATCH] ip_options_compile: properly handle unaligned pointer

[David Miller]

From: Chris Metcalf <cmetcalf@tilera.com>
Date: Sun, 29 May 2011 16:55:44 -0400

> The current code takes an unaligned pointer and does htonl() on it to
> make it big-endian, then does a memcpy().  The problem is that the
> compiler decides that since the pointer is to a __be32, it is legal
> to optimize the copy into a processor word store.  However, on an
> architecture that does not handled unaligned writes in kernel space,
> this produces an unaligned exception fault.
> 
> The solution is to track the pointer as a "char *" (which removes a bunch
> of unpleasant casts in any case), and then just use put_unaligned_be32()
> to write the value to memory.
> 
> Signed-off-by: Chris Metcalf <cmetcalf@tilera.com>

Applied, thanks Chris.