On 2026-07-09 21:36, David Gibson wrote:
On Thu, Jul 09, 2026 at 05:56:53PM -0400, Jon Maloy wrote:
In tap6_handler(), iov_tail_size(&data) - sizeof(*ip6h) computes the expected payload length. IOV_PEEK_HEADER() guarantees at least sizeof(*ip6h) bytes, but add an explicit check to guard the unsigned subtraction. A too-small tail would indicate a malformed packet, so skip it.
Signed-off-by: Jon Maloy
--- v2: Use if-guard instead of assert(), to avoid runtime cost in per-packet path and to let the static checker follow the logic.
I had the idea that the compiler may be smart enough to optimize it out, since it is logically redundant, as you note. /jon
Why would the if be cheaper than an assert()? The IOV_PEEK_HEADER() already checks the length, so this check is definitely redundant - it exists only for the benefit of static checkers.
--- tap.c | 5 ++++- 1 file changed, 4 insertions(+), 1 deletion(-)
diff --git a/tap.c b/tap.c index 6d93c7ce..6fd5f595 100644 --- a/tap.c +++ b/tap.c @@ -986,7 +986,10 @@ resume: if (!ip6h) continue;
- check = iov_tail_size(&data) - sizeof(*ip6h); + check = iov_tail_size(&data); + if (check < sizeof(*ip6h)) + continue; + check -= sizeof(*ip6h);
saddr = &ip6h->saddr; daddr = &ip6h->daddr; -- 2.52.0