netlink: call get_fd_nl_family before nlmsghdr decoding

Prepare for decoding of NETLINK_KOBJECT_UEVENT.  Messages of the latter,
unlike traditional netlink families, don't contain a header at all.

* netlink.c (NL_FAMILY_*): Remove enum.
(get_fd_nl_family): Replace NL_FAMILY_ERROR with -1.
(decode_nlmsg_type): Update the comment.
Skip family specific type decoders for type < NLMSG_MIN_TYPE.
(decode_nlmsghdr_with_payload): Skip family specific decoders
for type < NLMSG_MIN_TYPE && type != NLMSG_DONE.
(print_nlmsghdr): Move get_fd_nl_family invocation ...
(decode_nlmsghdr_with_payload): ... here.

diff --git a/netlink.c b/netlink.c
index f3a7cf9a8c42910db7b2edb9fbda73760dda38d8..eea75b6aaade34b7b82fb3001fdeefb4fe2cefa2 100644 (file)
--- a/netlink.c
+++ b/netlink.c
@@ -67,25 +67,20 @@ fetch_nlmsghdr(struct tcb *const tcp, struct nlmsghdr *const nlmsghdr,
        return true;
 }
 
-enum {
-       NL_FAMILY_ERROR = -1,
-       NL_FAMILY_DEFAULT = -2
-};
-
 static int
 get_fd_nl_family(struct tcb *const tcp, const int fd)
 {
        const unsigned long inode = getfdinode(tcp, fd);
        if (!inode)
-               return NL_FAMILY_ERROR;
+               return -1;
 
        const char *const details = get_sockaddr_by_inode(tcp, fd, inode);
        if (!details)
-               return NL_FAMILY_ERROR;
+               return -1;
 
        const char *const nl_details = STR_STRIP_PREFIX(details, "NETLINK:[");
        if (nl_details == details)
-               return NL_FAMILY_ERROR;
+               return -1;
 
        const struct xlat *xlats = netlink_protocols;
        for (; xlats->str; ++xlats) {
@@ -97,7 +92,7 @@ get_fd_nl_family(struct tcb *const tcp, const int fd)
        if (*nl_details >= '0' && *nl_details <= '9')
                return atoi(nl_details);
 
-       return NL_FAMILY_ERROR;
+       return -1;
 }
 
 static void
@@ -173,7 +168,7 @@ static const struct {
 
 /*
  * As all valid netlink families are positive integers, use unsigned int
- * for family here to filter out NL_FAMILY_ERROR and NL_FAMILY_DEFAULT.
+ * for family here to filter out -1.
  */
 static void
 decode_nlmsg_type(const uint16_t type, const unsigned int family)
@@ -182,7 +177,11 @@ decode_nlmsg_type(const uint16_t type, const unsigned int family)
        const struct xlat *xlat = netlink_types;
        const char *dflt = "NLMSG_???";
 
-       if (type != NLMSG_DONE && family < ARRAY_SIZE(nlmsg_types)) {
+       /*
+        * type < NLMSG_MIN_TYPE are reserved control messages
+        * that need no family-specific decoding.
+        */
+       if (type >= NLMSG_MIN_TYPE && family < ARRAY_SIZE(nlmsg_types)) {
                if (nlmsg_types[family].decoder)
                        decoder = nlmsg_types[family].decoder;
                if (nlmsg_types[family].xlat)
@@ -258,32 +257,24 @@ end:
        printflags_ex(flags, "NLM_F_???", netlink_flags, table, NULL);
 }
 
-static int
+static void
 print_nlmsghdr(struct tcb *tcp,
               const int fd,
-              int family,
+              const int family,
               const struct nlmsghdr *const nlmsghdr)
 {
        /* print the whole structure regardless of its nlmsg_len */
 
        tprintf("{len=%u, type=", nlmsghdr->nlmsg_len);
 
-       const int hdr_family = (nlmsghdr->nlmsg_type < NLMSG_MIN_TYPE
-                               && nlmsghdr->nlmsg_type != NLMSG_DONE)
-                              ? NL_FAMILY_DEFAULT
-                              : (family != NL_FAMILY_DEFAULT
-                                 ? family : get_fd_nl_family(tcp, fd));
-
-       decode_nlmsg_type(nlmsghdr->nlmsg_type, hdr_family);
+       decode_nlmsg_type(nlmsghdr->nlmsg_type, family);
 
        tprints(", flags=");
        decode_nlmsg_flags(nlmsghdr->nlmsg_flags,
-                          nlmsghdr->nlmsg_type, hdr_family);
+                          nlmsghdr->nlmsg_type, family);
 
        tprintf(", seq=%u, pid=%u}", nlmsghdr->nlmsg_seq,
                nlmsghdr->nlmsg_pid);
-
-       return family != NL_FAMILY_DEFAULT ? family : hdr_family;
 }
 
 static bool
@@ -319,7 +310,7 @@ static const nla_decoder_t nlmsgerr_nla_decoders[] = {
 static void
 decode_nlmsghdr_with_payload(struct tcb *const tcp,
                             const int fd,
-                            int family,
+                            const int family,
                             const struct nlmsghdr *const nlmsghdr,
                             const kernel_ulong_t addr,
                             const kernel_ulong_t len);
@@ -399,7 +390,18 @@ decode_payload(struct tcb *const tcp,
                return;
        }
 
-       if ((unsigned int) family < ARRAY_SIZE(netlink_decoders)
+       /*
+        * While most of NLMSG_DONE messages indeed have payloads
+        * containing just a single integer, there are few exceptions,
+        * so pass payloads of NLMSG_DONE messages to family-specific
+        * netlink payload decoders.
+        *
+        * Other types of reserved control messages need no family-specific
+        * netlink payload decoding.
+        */
+       if ((nlmsghdr->nlmsg_type >= NLMSG_MIN_TYPE
+           || nlmsghdr->nlmsg_type == NLMSG_DONE)
+           && (unsigned int) family < ARRAY_SIZE(netlink_decoders)
            && netlink_decoders[family]
            && netlink_decoders[family](tcp, nlmsghdr, addr, len)) {
                return;
@@ -419,7 +421,7 @@ decode_payload(struct tcb *const tcp,
 static void
 decode_nlmsghdr_with_payload(struct tcb *const tcp,
                             const int fd,
-                            int family,
+                            const int family,
                             const struct nlmsghdr *const nlmsghdr,
                             const kernel_ulong_t addr,
                             const kernel_ulong_t len)
@@ -430,7 +432,7 @@ decode_nlmsghdr_with_payload(struct tcb *const tcp,
        if (nlmsg_len > NLMSG_HDRLEN)
                tprints("{");
 
-       family = print_nlmsghdr(tcp, fd, family, nlmsghdr);
+       print_nlmsghdr(tcp, fd, family, nlmsghdr);
 
        if (nlmsg_len > NLMSG_HDRLEN) {
                tprints(", ");
@@ -446,6 +448,7 @@ decode_netlink(struct tcb *const tcp,
               kernel_ulong_t addr,
               kernel_ulong_t len)
 {
+       const int family = get_fd_nl_family(tcp, fd);
        struct nlmsghdr nlmsghdr;
        bool print_array = false;
        unsigned int elt;
@@ -472,7 +475,7 @@ decode_netlink(struct tcb *const tcp,
                        print_array = true;
                }
 
-               decode_nlmsghdr_with_payload(tcp, fd, NL_FAMILY_DEFAULT,
+               decode_nlmsghdr_with_payload(tcp, fd, family,
                                             &nlmsghdr, addr, len);
 
                if (!next_addr)