udp_io: fix two more potential cases of unaligned accesses. 0 code size changes.

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>

1 files changed, 32 insertions, 21 deletions

diff --git a/libbb/udp_io.c b/libbb/udp_io.c
index b31f28416..d9375eac2 100644
--- a/libbb/udp_io.c
+++ b/libbb/udp_io.c
@@ -6,7 +6,6 @@
  *
  * Licensed under GPL version 2, see file LICENSE in this tarball for details.
  */
-
 #include "libbb.h"
 
 /*
@@ -32,22 +31,23 @@ send_to_from(int fd, void *buf, size_t len, int flags,
                 socklen_t tolen)
 {
 #ifndef IP_PKTINFO
+        (void)from; /* suppress "unused from" warning */
         return sendto(fd, buf, len, flags, to, tolen);
 #else
         struct iovec iov[1];
         struct msghdr msg;
         union {
                 char cmsg[CMSG_SPACE(sizeof(struct in_pktinfo))];
-#if ENABLE_FEATURE_IPV6 && defined(IPV6_PKTINFO)
+# if ENABLE_FEATURE_IPV6 && defined(IPV6_PKTINFO)
                 char cmsg6[CMSG_SPACE(sizeof(struct in6_pktinfo))];
-#endif
+# endif
         } u;
         struct cmsghdr* cmsgptr;
 
         if (from->sa_family != AF_INET
-#if ENABLE_FEATURE_IPV6
+# if ENABLE_FEATURE_IPV6
          && from->sa_family != AF_INET6
-#endif
+# endif
         ) {
                 /* ANY local address */
                 return sendto(fd, buf, len, flags, to, tolen);
@@ -76,20 +76,26 @@ send_to_from(int fd, void *buf, size_t len, int flags,
                 cmsgptr->cmsg_type = IP_PKTINFO;
                 cmsgptr->cmsg_len = CMSG_LEN(sizeof(struct in_pktinfo));
                 pktptr = (struct in_pktinfo *)(CMSG_DATA(cmsgptr));
-                /* pktptr->ipi_ifindex = 0; -- already done by memset(cbuf...) */
+                /*pktptr->ipi_ifindex = 0; -- already done by memset(u...) */
+                /* In general, CMSG_DATA() can be unaligned, but in this case
+                 * we know for sure it is sufficiently aligned:
+                 * CMSG_FIRSTHDR simply returns &u above,
+                 * and CMSG_DATA returns &u + size_t + int + int.
+                 * Thus direct assignment is ok:
+                 */
                 pktptr->ipi_spec_dst = ((struct sockaddr_in*)from)->sin_addr;
         }
-#if ENABLE_FEATURE_IPV6 && defined(IPV6_PKTINFO)
+# if ENABLE_FEATURE_IPV6 && defined(IPV6_PKTINFO)
         else if (to->sa_family == AF_INET6 && from->sa_family == AF_INET6) {
                 struct in6_pktinfo *pktptr;
                 cmsgptr->cmsg_level = IPPROTO_IPV6;
                 cmsgptr->cmsg_type = IPV6_PKTINFO;
                 cmsgptr->cmsg_len = CMSG_LEN(sizeof(struct in6_pktinfo));
                 pktptr = (struct in6_pktinfo *)(CMSG_DATA(cmsgptr));
-                /* pktptr->ipi6_ifindex = 0; -- already done by memset(cbuf...) */
+                /* pktptr->ipi6_ifindex = 0; -- already done by memset(u...) */
                 pktptr->ipi6_addr = ((struct sockaddr_in6*)from)->sin6_addr;
         }
-#endif
+# endif
         msg.msg_controllen = cmsgptr->cmsg_len;
 
         return sendmsg(fd, &msg, flags);
@@ -106,15 +112,16 @@ recv_from_to(int fd, void *buf, size_t len, int flags,
                 socklen_t sa_size)
 {
 #ifndef IP_PKTINFO
+        (void)to; /* suppress "unused to" warning */
         return recvfrom(fd, buf, len, flags, from, &sa_size);
 #else
         /* man recvmsg and man cmsg is needed to make sense of code below */
         struct iovec iov[1];
         union {
                 char cmsg[CMSG_SPACE(sizeof(struct in_pktinfo))];
-#if ENABLE_FEATURE_IPV6 && defined(IPV6_PKTINFO)
+# if ENABLE_FEATURE_IPV6 && defined(IPV6_PKTINFO)
                 char cmsg6[CMSG_SPACE(sizeof(struct in6_pktinfo))];
-#endif
+# endif
         } u;
         struct cmsghdr *cmsgptr;
         struct msghdr msg;
@@ -135,6 +142,8 @@ recv_from_to(int fd, void *buf, size_t len, int flags,
         if (recv_length < 0)
                 return recv_length;
 
+# define to4 ((struct sockaddr_in*)to)
+# define to6 ((struct sockaddr_in6*)to)
         /* Here we try to retrieve destination IP and memorize it */
         for (cmsgptr = CMSG_FIRSTHDR(&msg);
                         cmsgptr != NULL;
@@ -143,25 +152,27 @@ recv_from_to(int fd, void *buf, size_t len, int flags,
                 if (cmsgptr->cmsg_level == IPPROTO_IP
                  && cmsgptr->cmsg_type == IP_PKTINFO
                 ) {
-#define pktinfo(cmsgptr) ( (struct in_pktinfo*)(CMSG_DATA(cmsgptr)) )
+# define pktinfo(cmsgptr) ( (struct in_pktinfo*)(CMSG_DATA(cmsgptr)) )
                         to->sa_family = AF_INET;
-                        ((struct sockaddr_in*)to)->sin_addr = pktinfo(cmsgptr)->ipi_addr;
-                        /* ((struct sockaddr_in*)to)->sin_port = 123; */
-#undef pktinfo
+                        /*to4->sin_addr = pktinfo(cmsgptr)->ipi_addr; - may be unaligned */
+                        memcpy(&to4->sin_addr, &pktinfo(cmsgptr)->ipi_addr, sizeof(to4->sin_addr));
+                        /*to4->sin_port = 123; - this data is not supplied by kernel */
+# undef pktinfo
                         break;
                 }
-#if ENABLE_FEATURE_IPV6 && defined(IPV6_PKTINFO)
+# if ENABLE_FEATURE_IPV6 && defined(IPV6_PKTINFO)
                 if (cmsgptr->cmsg_level == IPPROTO_IPV6
                  && cmsgptr->cmsg_type == IPV6_PKTINFO
                 ) {
-#define pktinfo(cmsgptr) ( (struct in6_pktinfo*)(CMSG_DATA(cmsgptr)) )
+#  define pktinfo(cmsgptr) ( (struct in6_pktinfo*)(CMSG_DATA(cmsgptr)) )
                         to->sa_family = AF_INET6;
-                        ((struct sockaddr_in6*)to)->sin6_addr = pktinfo(cmsgptr)->ipi6_addr;
-                        /* ((struct sockaddr_in6*)to)->sin6_port = 123; */
-#undef pktinfo
+                        /*to6->sin6_addr = pktinfo(cmsgptr)->ipi6_addr; - may be unaligned */
+                        memcpy(&to6->sin6_addr, &pktinfo(cmsgptr)->ipi6_addr, sizeof(to6->sin6_addr));
+                        /*to6->sin6_port = 123; */
+#  undef pktinfo
                         break;
                 }
-#endif
+# endif
         }
         return recv_length;
 #endif