ndp: Fix Clang analyzer warning (clang-analyzer-security.PointerSub)

Addresses Clang warning: "Subtraction of two pointers that do not
point into the same array is undefined behavior" for the line:
  `ndp_send(c, dst, &ra, ptr - (unsigned char *)&ra);`

Here, `ptr` is `&ra.var[0]`. The subtraction calculates the offset
of `var[0]` within the `struct ra_options ra`. Since `ptr` points
inside `ra`, this pointer arithmetic is well-defined for
calculating the size of the data to send, even if `ptr` and `&ra`
are not strictly considered part of the same "array" by the analyzer.

Signed-off-by: Laurent Vivier <lvivier@redhat.com>
Signed-off-by: Stefano Brivio <sbrivio@redhat.com>

1 files changed, 1 insertions, 0 deletions

diff --git a/ndp.c b/ndp.c
index ded2081..b664034 100644
--- a/ndp.c
+++ b/ndp.c
@@ -328,6 +328,7 @@ static void ndp_ra(const struct ctx *c, const struct in6_addr *dst)
 
 	memcpy(&ra.source_ll.mac, c->our_tap_mac, ETH_ALEN);
 
+	/* NOLINTNEXTLINE(clang-analyzer-security.PointerSub) */
 	ndp_send(c, dst, &ra, ptr - (unsigned char *)&ra);
 }