[PATCH AUTOSEL 4.9 3/5] netfilter: nf_tables: Allow set back-ends to report partial overlaps on insertion

[Sasha Levin]

From: Pablo Neira Ayuso <pablo@xxxxxxxxxxxxx>

[ Upstream commit 8c2d45b2b65ca1f215244be1c600236e83f9815f ]

Currently, the -EEXIST return code of ->insert() callbacks is ambiguous: it
might indicate that a given element (including intervals) already exists as
such, or that the new element would clash with existing ones.

If identical elements already exist, the front-end is ignoring this without
returning error, in case NLM_F_EXCL is not set. However, if the new element
can't be inserted due an overlap, we should report this to the user.

To this purpose, allow set back-ends to return -ENOTEMPTY on collision with
existing elements, translate that to -EEXIST, and return that to userspace,
no matter if NLM_F_EXCL was set.

Reported-by: Phil Sutter <phil@xxxxxx>
Signed-off-by: Stefano Brivio <sbrivio@xxxxxxxxxx>
Signed-off-by: Pablo Neira Ayuso <pablo@xxxxxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
---
 net/netfilter/nf_tables_api.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/net/netfilter/nf_tables_api.c b/net/netfilter/nf_tables_api.c
index 2fa1c4f2e94e0..d9b448ed9a47c 100644
--- a/net/netfilter/nf_tables_api.c
+++ b/net/netfilter/nf_tables_api.c
@@ -3642,6 +3642,11 @@ static int nft_add_set_elem(struct nft_ctx *ctx, struct nft_set *set,
 				err = -EBUSY;
 			else if (!(nlmsg_flags & NLM_F_EXCL))
 				err = 0;
+		} else if (err == -ENOTEMPTY) {
+			/* ENOTEMPTY reports overlapping between this element
+			 * and an existing one.
+			 */
+			err = -EEXIST;
 		}
 		goto err5;
 	}
-- 
2.20.1