[iptables PATCH 4/4] nft: Fix EPERM handling for extensions without rev 0

[Phil Sutter <phil@nwl.cc>]

Treating revision 0 as compatible in EPERM case works fine as long as
there is a revision 0 of that extension defined in DSO. Fix the code for
others: Extend the EPERM handling to all revisions and keep the existing
warning for revision 0.

Fixes: 17534cb18ed0a ("Improve error messages for unsupported extensions")
Signed-off-by: Phil Sutter <phil@nwl.cc>
---
 iptables/nft.c                                     | 14 ++++++++++----
 .../shell/testcases/iptables/0008-unprivileged_0   |  6 ++++++
 2 files changed, 16 insertions(+), 4 deletions(-)

diff --git a/iptables/nft.c b/iptables/nft.c
index 33813ce1b9202..95e6c222682c0 100644
--- a/iptables/nft.c
+++ b/iptables/nft.c
@@ -3510,15 +3510,21 @@ int nft_compatible_revision(const char *name, uint8_t rev, int opt)
 err:
 	mnl_socket_close(nl);
 
-	/* pretend revision 0 is valid -
+	/* ignore EPERM and errors for revision 0 -
 	 * this is required for printing extension help texts as user, also
 	 * helps error messaging on unavailable kernel extension */
-	if (ret < 0 && rev == 0) {
-		if (errno != EPERM)
+	if (ret < 0) {
+		if (errno == EPERM) {
+			fprintf(stderr,
+				"%s: Could not determine whether revision %u is supported, assuming it is.\n",
+				name, rev);
+			return 1;
+		} else if (rev == 0) {
 			fprintf(stderr,
 				"Warning: Extension %s revision 0 not supported, missing kernel module?\n",
 				name);
-		return 1;
+			return 1;
+		}
 	}
 
 	return ret < 0 ? 0 : 1;
diff --git a/iptables/tests/shell/testcases/iptables/0008-unprivileged_0 b/iptables/tests/shell/testcases/iptables/0008-unprivileged_0
index 43e3bc8721dbd..983531fef4720 100755
--- a/iptables/tests/shell/testcases/iptables/0008-unprivileged_0
+++ b/iptables/tests/shell/testcases/iptables/0008-unprivileged_0
@@ -35,6 +35,12 @@ let "rc+=$?"
 grep_or_rc "DNAT target options:" <<< "$out"
 let "rc+=$?"
 
+# TEE has no revision 0
+out=$(run $XT_MULTI iptables -j TEE --help)
+let "rc+=$?"
+grep_or_rc "TEE target options:" <<< "$out"
+let "rc+=$?"
+
 out=$(run $XT_MULTI iptables -p tcp -j DNAT --help)
 let "rc+=$?"
 grep_or_rc "tcp match options:" <<< "$out"
-- 
2.34.1