net: sched: cls_api: improve the error message for ID allocation failure

We run into an exhaustion problem with the kernel-allocated filter IDs.
Our allocation problem can be fixed on the user space side,
but the error message in this case was quite misleading:

  "Filter with specified priority/protocol not found" (EINVAL)

Specifically when we can't allocate a _new_ ID because filter with
lowest ID already _exists_, saying "filter not found", is confusing.

Kernel allocates IDs in range of 0xc0000 -> 0x8000, giving out ID one
lower than lowest existing in that range. The error message makes sense
when tcf_chain_tp_find() gets called for GET and DEL but for NEW we
need to provide more specific error messages for all three cases:

 - user wants the ID to be auto-allocated but filter with ID 0x8000
   already exists

 - filter already exists and can be replaced, but user asked
   for a protocol change

 - filter doesn't exist

Caller of tcf_chain_tp_insert_unique() doesn't set extack today,
so don't bother plumbing it in.

Reviewed-by: Simon Horman <horms@kernel.org>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Acked-by: Jamal Hadi Salim <jhs@mojatatu.com>
Link: https://patch.msgid.link/20241108010254.2995438-1-kuba@kernel.org
Signed-off-by: Paolo Abeni <pabeni@redhat.com>

diff --git a/net/sched/cls_api.c b/net/sched/cls_api.c
index 04942f8c62e0f851deb4843d9ba28ecd1c2c4c6d..7578e27260c9bb78b6efa428e64a5b13b074833a 100644 (file)
--- a/net/sched/cls_api.c
+++ b/net/sched/cls_api.c
@@ -1933,7 +1933,8 @@ static void tcf_chain_tp_remove(struct tcf_chain *chain,
 static struct tcf_proto *tcf_chain_tp_find(struct tcf_chain *chain,
                                           struct tcf_chain_info *chain_info,
                                           u32 protocol, u32 prio,
-                                          bool prio_allocate);
+                                          bool prio_allocate,
+                                          struct netlink_ext_ack *extack);
 
 /* Try to insert new proto.
  * If proto with specified priority already exists, free new proto
@@ -1957,8 +1958,7 @@ static struct tcf_proto *tcf_chain_tp_insert_unique(struct tcf_chain *chain,
                return ERR_PTR(-EAGAIN);
        }
 
-       tp = tcf_chain_tp_find(chain, &chain_info,
-                              protocol, prio, false);
+       tp = tcf_chain_tp_find(chain, &chain_info, protocol, prio, false, NULL);
        if (!tp)
                err = tcf_chain_tp_insert(chain, &chain_info, tp_new);
        mutex_unlock(&chain->filter_chain_lock);
@@ -2018,7 +2018,8 @@ static void tcf_chain_tp_delete_empty(struct tcf_chain *chain,
 static struct tcf_proto *tcf_chain_tp_find(struct tcf_chain *chain,
                                           struct tcf_chain_info *chain_info,
                                           u32 protocol, u32 prio,
-                                          bool prio_allocate)
+                                          bool prio_allocate,
+                                          struct netlink_ext_ack *extack)
 {
        struct tcf_proto **pprev;
        struct tcf_proto *tp;
@@ -2029,9 +2030,14 @@ static struct tcf_proto *tcf_chain_tp_find(struct tcf_chain *chain,
             pprev = &tp->next) {
                if (tp->prio >= prio) {
                        if (tp->prio == prio) {
-                               if (prio_allocate ||
-                                   (tp->protocol != protocol && protocol))
+                               if (prio_allocate) {
+                                       NL_SET_ERR_MSG(extack, "Lowest ID from auto-alloc range already in use");
+                                       return ERR_PTR(-ENOSPC);
+                               }
+                               if (tp->protocol != protocol && protocol) {
+                                       NL_SET_ERR_MSG(extack, "Protocol mismatch for filter with specified priority");
                                        return ERR_PTR(-EINVAL);
+                               }
                        } else {
                                tp = NULL;
                        }
@@ -2312,9 +2318,8 @@ replay:
 
        mutex_lock(&chain->filter_chain_lock);
        tp = tcf_chain_tp_find(chain, &chain_info, protocol,
-                              prio, prio_allocate);
+                              prio, prio_allocate, extack);
        if (IS_ERR(tp)) {
-               NL_SET_ERR_MSG(extack, "Filter with specified priority/protocol not found");
                err = PTR_ERR(tp);
                goto errout_locked;
        }
@@ -2539,10 +2544,13 @@ static int tc_del_tfilter(struct sk_buff *skb, struct nlmsghdr *n,
 
        mutex_lock(&chain->filter_chain_lock);
        tp = tcf_chain_tp_find(chain, &chain_info, protocol,
-                              prio, false);
-       if (!tp || IS_ERR(tp)) {
+                              prio, false, extack);
+       if (!tp) {
+               err = -ENOENT;
                NL_SET_ERR_MSG(extack, "Filter with specified priority/protocol not found");
-               err = tp ? PTR_ERR(tp) : -ENOENT;
+               goto errout_locked;
+       } else if (IS_ERR(tp)) {
+               err = PTR_ERR(tp);
                goto errout_locked;
        } else if (tca[TCA_KIND] && nla_strcmp(tca[TCA_KIND], tp->ops->kind)) {
                NL_SET_ERR_MSG(extack, "Specified filter kind does not match existing one");
@@ -2679,11 +2687,14 @@ static int tc_get_tfilter(struct sk_buff *skb, struct nlmsghdr *n,
 
        mutex_lock(&chain->filter_chain_lock);
        tp = tcf_chain_tp_find(chain, &chain_info, protocol,
-                              prio, false);
+                              prio, false, extack);
        mutex_unlock(&chain->filter_chain_lock);
-       if (!tp || IS_ERR(tp)) {
+       if (!tp) {
+               err = -ENOENT;
                NL_SET_ERR_MSG(extack, "Filter with specified priority/protocol not found");
-               err = tp ? PTR_ERR(tp) : -ENOENT;
+               goto errout;
+       } else if (IS_ERR(tp)) {
+               err = PTR_ERR(tp);
                goto errout;
        } else if (tca[TCA_KIND] && nla_strcmp(tca[TCA_KIND], tp->ops->kind)) {
                NL_SET_ERR_MSG(extack, "Specified filter kind does not match existing one");