Commit ac0dbed9 authored by Nick Desaulniers's avatar Nick Desaulniers Committed by Jakub Kicinski

net: seg6: initialize induction variable to first valid array index

Fixes the following warnings observed when building
CONFIG_IPV6_SEG6_LWTUNNEL=y with clang:

  net/ipv6/seg6_local.o: warning: objtool: seg6_local_fill_encap() falls
  through to next function seg6_local_get_encap_size()
  net/ipv6/seg6_local.o: warning: objtool: seg6_local_cmp_encap() falls
  through to next function input_action_end()

LLVM can fully unroll loops in seg6_local_get_encap_size() and
seg6_local_cmp_encap(). One issue in those loops is that the induction
variable is initialized to 0. The loop iterates over members of
seg6_action_params, a global array of struct seg6_action_param calling
their put() function pointer members.  seg6_action_param uses an array
initializer to initialize SEG6_LOCAL_SRH and later elements, which is
the third enumeration of an anonymous union.

The guard `if (attrs & SEG6_F_ATTR(i))` may prevent this from being
called at runtime, but it would still be UB for
`seg6_action_params[0]->put` to be called; the unrolled loop will make
the initial iterations unreachable, which LLVM will later rotate to
fallthrough to the next function.

Make this more obvious that this cannot happen to the compiler by
initializing the loop induction variable to the minimum valid index that
seg6_action_params is initialized to.
Reported-by: default avatarThomas Gleixner <tglx@linutronix.de>
Signed-off-by: default avatarNick Desaulniers <ndesaulniers@google.com>
Link: https://lore.kernel.org/r/20220802161203.622293-1-ndesaulniers@google.comSigned-off-by: default avatarJakub Kicinski <kuba@kernel.org>
parent bc3410f2
......@@ -1614,7 +1614,7 @@ static void __destroy_attrs(unsigned long parsed_attrs, int max_parsed,
* callback. If the callback is not available, then we skip to the next
* attribute; otherwise, we call the destroy() callback.
*/
for (i = 0; i < max_parsed; ++i) {
for (i = SEG6_LOCAL_SRH; i < max_parsed; ++i) {
if (!(parsed_attrs & SEG6_F_ATTR(i)))
continue;
......@@ -1643,7 +1643,7 @@ static int parse_nla_optional_attrs(struct nlattr **attrs,
struct seg6_action_param *param;
int err, i;
for (i = 0; i < SEG6_LOCAL_MAX + 1; ++i) {
for (i = SEG6_LOCAL_SRH; i < SEG6_LOCAL_MAX + 1; ++i) {
if (!(desc->optattrs & SEG6_F_ATTR(i)) || !attrs[i])
continue;
......@@ -1742,7 +1742,7 @@ static int parse_nla_action(struct nlattr **attrs, struct seg6_local_lwt *slwt)
}
/* parse the required attributes */
for (i = 0; i < SEG6_LOCAL_MAX + 1; i++) {
for (i = SEG6_LOCAL_SRH; i < SEG6_LOCAL_MAX + 1; i++) {
if (desc->attrs & SEG6_F_ATTR(i)) {
if (!attrs[i])
return -EINVAL;
......@@ -1847,7 +1847,7 @@ static int seg6_local_fill_encap(struct sk_buff *skb,
attrs = slwt->desc->attrs | slwt->parsed_optattrs;
for (i = 0; i < SEG6_LOCAL_MAX + 1; i++) {
for (i = SEG6_LOCAL_SRH; i < SEG6_LOCAL_MAX + 1; i++) {
if (attrs & SEG6_F_ATTR(i)) {
param = &seg6_action_params[i];
err = param->put(skb, slwt);
......@@ -1927,7 +1927,7 @@ static int seg6_local_cmp_encap(struct lwtunnel_state *a,
if (attrs_a != attrs_b)
return 1;
for (i = 0; i < SEG6_LOCAL_MAX + 1; i++) {
for (i = SEG6_LOCAL_SRH; i < SEG6_LOCAL_MAX + 1; i++) {
if (attrs_a & SEG6_F_ATTR(i)) {
param = &seg6_action_params[i];
if (param->cmp(slwt_a, slwt_b))
......
Markdown is supported
0%
or
You are about to add 0 people to the discussion. Proceed with caution.
Finish editing this message first!
Please register or to comment