Brett A C Sheffield wrote:
Add selftest for the IPv6 fragmentation regression which affected several stable kernels.
Commit a18dfa9925b9 ("ipv6: save dontfrag in cork") was backported to stable without some prerequisite commits. This caused a regression when sending IPv6 UDP packets by preventing fragmentation and instead returning -1 (EMSGSIZE).
Add selftest to check for this issue by attempting to send a packet larger than the interface MTU. The packet will be fragmented on a working kernel, with sendmsg(2) correctly returning the expected number of bytes sent. When the regression is present, sendmsg returns -1 and sets errno to EMSGSIZE.
Link: https://lore.kernel.org/stable/aElivdUXqd1OqgMY@karahi.gladserv.com Signed-off-by: Brett A C Sheffield bacs@librecast.net
Reviewed-by: Willem de Bruijn willemb@google.com
v4 changes:
- fix "else should follow close brace" (checkpatch ERROR)
Reminder to send only only iteration to netdev per 24 hrs.
v3 changes:
- add usleep instead of busy polling on sendmsg
- simplify error handling by using error() and leaving cleanup to O/S
- use loopback interface - don't bother creating TAP
- send to localhost (::1)
+/* no need to wait for DAD in our namespace */ +static int disable_dad(char *ifname) +{
- char sysvar[] = "/proc/sys/net/ipv6/conf/%s/accept_dad";
- char fname[IFNAMSIZ + sizeof(sysvar)];
- int fd;
- snprintf(fname, sizeof(fname), sysvar, ifname);
- fd = open(fname, O_WRONLY);
- if (fd == -1)
error(KSFT_FAIL, errno, "open accept_dad");- if (write(fd, "0", 1) != 1)
error(KSFT_FAIL, errno, "write accept_dad");- return close(fd);
+}
Is this needed with loopback?
+int main(void) +{
- struct in6_addr addr = {
.s6_addr[15] = 0x01, /* ::1 */- };
- struct sockaddr_in6 sa = {
.sin6_family = AF_INET6,.sin6_addr = addr,.sin6_port = 9 /* port 9/udp (DISCARD) */
htons
- };
- char buf[LARGER_THAN_MTU] = {0};
That's a large stack allocation. static char?
- ns_fd = setup();
- s = socket(AF_INET6, SOCK_DGRAM, 0);
+send_again:
- rc = sendmsg(s, &msg, 0);
- if (rc == -1) {
/* if interface wasn't ready, try again */if (errno == EADDRNOTAVAIL) {usleep(1000);goto send_again;}printf("[FAIL] sendmsg: %s\n", strerror(errno));- } else if (rc != LARGER_THAN_MTU) {
printf("[FAIL] sendmsg() returned %zi, expected %i\n", rc, LARGER_THAN_MTU);- } else {
printf("[PASS] sendmsg() returned %zi\n", rc);err = KSFT_PASS;
slight preference to just fail with error() in the two error cases and let the expected common path be linear and succeed:
if (rc == -1) { if (..) goto send_again; error(KSFT_FAIL, ..); } if (rc != LARGER_THAN_MTU) { error(KSFT_FAIL, ..); }
printf(..) return KSFT_PASS;
- }
- close(s);
- close(ns_fd);
ns_fd is always -1. Check all system calls return values. Now that setup internally can fail with error() no need for return values at all.
- return err;
+}
base-commit: 864ecc4a6dade82d3f70eab43dad0e277aa6fc78
2.49.1