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* FAILED: patch "[PATCH] selftests/landlock: Fix snprintf truncation checks in test files" failed to apply to 6.18-stable tree
@ 2026-11-07 10:13 Sasha Levin
  2026-11-11  2:17 ` [PATCH 6.18.y] selftests/landlock: Fix snprintf truncation checks in test files Sasha Levin
  0 siblings, 1 reply; 2+ messages in thread
From: Sasha Levin @ 2026-11-07 10:13 UTC (permalink / raw)
  To: wangyan01, lihaofeng, gnoack, mic; +Cc: stable

The patch below does not apply to the 6.18-stable tree.
If someone wants it applied there, or to any other stable or longterm
tree, then please email the backport, including the original git commit
id to <stable@vger.kernel.org>.

To reproduce the conflict and resubmit, you may use the following commands:

git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-6.18.y
git checkout FETCH_HEAD
git cherry-pick -x 8e4c736cffdd6b133f6498e0d40ba60dc6819d43
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<stable@vger.kernel.org>' --in-reply-to '20261107051310-failed-6.18-8e4c736cffdd@kernel.org' --subject-prefix 'PATCH 6.18.y' 'HEAD^..'

Thanks,
Sasha

------------------ original commit in Linus's tree ------------------

From 8e4c736cffdd6b133f6498e0d40ba60dc6819d43 Mon Sep 17 00:00:00 2001
From: Wang Yan <wangyan01@kylinos.cn>
Date: Fri, 26 Jun 2026 15:00:16 +0800
Subject: [PATCH] selftests/landlock: Fix snprintf truncation checks in test
 files
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

Commit b566f7a4f0e4 ("selftests/landlock: Fix snprintf truncation checks
in audit helpers") fixed the truncation detection in audit.h by changing
the comparison from ">" to ">=" to correctly handle the edge case where
snprintf returns a value equal to the buffer size.

However, the same pattern exists in ptrace_test.c, audit_test.c, and
net_test.c and was not fixed.  snprintf() returns the number of
characters that would have been written, excluding the terminating NUL
byte.  When the output is truncated, this return value equals or exceeds
the buffer size. The existing ">" check therefore fails to detect
truncation when the return value equals the buffer size.

Fix these remaining instances to use ">=" for truncation detection,
matching the fix in audit.h.

Fixes: 6a500b22971c ("selftests/landlock: Add tests for audit flags and domain IDs")
Signed-off-by: Haofeng Li <lihaofeng@kylinos.cn>
Signed-off-by: Wang Yan <wangyan01@kylinos.cn>
Reviewed-by: Günther Noack <gnoack@google.com>
Link: https://patch.msgid.link/20260626070016.61049-1-wangyan01@kylinos.cn
Cc: stable@vger.kernel.org
Signed-off-by: Mickaël Salaün <mic@digikod.net>
---
 tools/testing/selftests/landlock/audit_test.c  | 2 +-
 tools/testing/selftests/landlock/net_test.c    | 4 ++--
 tools/testing/selftests/landlock/ptrace_test.c | 2 +-
 3 files changed, 4 insertions(+), 4 deletions(-)

diff --git a/tools/testing/selftests/landlock/audit_test.c b/tools/testing/selftests/landlock/audit_test.c
index 72b5612375ddb..4bea8c880a4d3 100644
--- a/tools/testing/selftests/landlock/audit_test.c
+++ b/tools/testing/selftests/landlock/audit_test.c
@@ -31,7 +31,7 @@ static int matches_log_signal(struct __test_metadata *const _metadata,
 
 	log_match_len =
 		snprintf(log_match, sizeof(log_match), log_template, opid);
-	if (log_match_len > sizeof(log_match))
+	if (log_match_len >= sizeof(log_match))
 		return -E2BIG;
 
 	return audit_match_record(audit_fd, AUDIT_LANDLOCK_ACCESS, log_match,
diff --git a/tools/testing/selftests/landlock/net_test.c b/tools/testing/selftests/landlock/net_test.c
index 16afbfdf06bb2..50b637354b51d 100644
--- a/tools/testing/selftests/landlock/net_test.c
+++ b/tools/testing/selftests/landlock/net_test.c
@@ -2878,7 +2878,7 @@ static int matches_auditlog(const int audit_fd, const char *const blockers,
 		log_match_len = snprintf(log_match, sizeof(log_match),
 					 log_with_addrport_tmpl, blockers,
 					 dir_addr, addr, dir_port, port);
-	if (log_match_len > sizeof(log_match))
+	if (log_match_len >= sizeof(log_match))
 		return -E2BIG;
 
 	return audit_match_record(audit_fd, AUDIT_LANDLOCK_ACCESS, log_match,
@@ -3173,7 +3173,7 @@ static int matches_log_connect_bound(int audit_fd, const char *const blockers,
 
 	log_match_len = snprintf(log_match, sizeof(log_match), log_template,
 				 blockers, addr, lport, addr, dport);
-	if (log_match_len > sizeof(log_match))
+	if (log_match_len >= sizeof(log_match))
 		return -E2BIG;
 
 	return audit_match_record(audit_fd, AUDIT_LANDLOCK_ACCESS, log_match,
diff --git a/tools/testing/selftests/landlock/ptrace_test.c b/tools/testing/selftests/landlock/ptrace_test.c
index 2644445a9d020..e0e7f95e889b3 100644
--- a/tools/testing/selftests/landlock/ptrace_test.c
+++ b/tools/testing/selftests/landlock/ptrace_test.c
@@ -305,7 +305,7 @@ static int matches_log_ptrace(struct __test_metadata *const _metadata,
 
 	log_match_len =
 		snprintf(log_match, sizeof(log_match), log_template, opid);
-	if (log_match_len > sizeof(log_match))
+	if (log_match_len >= sizeof(log_match))
 		return -E2BIG;
 
 	return audit_match_record(audit_fd, AUDIT_LANDLOCK_ACCESS, log_match,
-- 
2.53.0





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2026-11-11  2:17 ` [PATCH 6.18.y] selftests/landlock: Fix snprintf truncation checks in test files Sasha Levin

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