ip: fix UB in strncpy (e.g. truncated ip route output)

Fix overlapping buffers passed to strncpy which is UB. format_host_rta_r writes
to the buffer passed to it, so hostname (derived from b1) & b1 partly overlap.

This gets worse with sys-libs/glibc-2.37 where the ip route output can be truncated,
but it was UB anyway and you can see it occurring w/ glibc-2.36.

Bug: https://lore.kernel.org/netdev/0011AC38-4823-4D0A-8580-B108D08959C2@gentoo.org/T/#u
Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=30112
Thanks-to: Doug Freed <dwfreed@mtu.edu>
Signed-off-by: Sam James <sam@gentoo.org>
Signed-off-by: Stephen Hemminger <stephen@networkplumber.org>

diff --git a/ip/iproute.c b/ip/iproute.c
index 0bab0fdfae136a4ce52c07a80c37bf325dd36ec4..a7cd9543af810797400f9569c57d3a600d3d9ff3 100644 (file)
--- a/ip/iproute.c
+++ b/ip/iproute.c
@@ -748,6 +748,7 @@ int print_route(struct nlmsghdr *n, void *arg)
        int ret;
 
        SPRINT_BUF(b1);
+       SPRINT_BUF(b2);
 
        if (n->nlmsg_type != RTM_NEWROUTE && n->nlmsg_type != RTM_DELROUTE) {
                fprintf(stderr, "Not a route: %08x %08x %08x\n",
@@ -809,7 +810,7 @@ int print_route(struct nlmsghdr *n, void *arg)
                                 r->rtm_dst_len);
                } else {
                        const char *hostname = format_host_rta_r(family, tb[RTA_DST],
-                                         b1, sizeof(b1));
+                                         b2, sizeof(b2));
                        if (hostname)
                                strncpy(b1, hostname, sizeof(b1) - 1);
                }
@@ -832,7 +833,7 @@ int print_route(struct nlmsghdr *n, void *arg)
                                 r->rtm_src_len);
                } else {
                        const char *hostname = format_host_rta_r(family, tb[RTA_SRC],
-                                         b1, sizeof(b1));
+                                         b2, sizeof(b2));
                        if (hostname)
                                strncpy(b1, hostname, sizeof(b1) - 1);
                }