python3-idna: Fix CVE-2026-45409

This patch applies the complete upstream fix chain for
CVE-2026-45409. Commit [1] introduces early domain-length rejection
required by [2]. Commit [2] is the v3.14 fix identified by [5], and
commit [3] extends the protection to per-label conversions and codec
support to complete the v3.15 fix described in [4].

[1] https://github.com/kjd/idna/commit/c0dda4501df5
[2] https://github.com/kjd/idna/commit/628fef84d3ed
[3] https://github.com/kjd/idna/commit/e1cb465b6376
[4] https://github.com/kjd/idna/security/advisories/GHSA-65pc-fj4g-8rjx
[5] https://security-tracker.debian.org/tracker/CVE-2026-45409

(From OE-Core rev: 09773d9d1b44dfe868913b6bb142a728529f62cb)

Signed-off-by: Hetvi Thakar <hthakar@cisco.com>
Signed-off-by: Yoann Congal <yoann.congal@smile.fr>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

meta/recipes-devtools/python/python3-idna/CVE-2026-45409_p1.patch

@@ -0,0 +1,75 @@
+From b34cd8399981324b361ae4f2b8e0eb77444ae0e3 Mon Sep 17 00:00:00 2001
+From: Kim Davies <kim@cynosure.com.au>
+Date: Sun, 10 May 2026 08:47:22 -0700
+Subject: [PATCH 1/3] Merge commit from fork
+
+CVE: CVE-2026-45409
+Upstream-Status: Backport [https://github.com/kjd/idna/commit/c0dda4501df5d91c3181ce6f962dc5de74e82cc1]
+
+Backport Changes:
+- Omit the HISTORY.rst hunk because it documents the upstream 3.14
+  release and is not applicable to the Scarthgap 3.7 source.
+
+(cherry picked from commit c0dda4501df5d91c3181ce6f962dc5de74e82cc1)
+Signed-off-by: Hetvi Thakar <hthakar@cisco.com>
+---
+ idna/core.py       | 14 ++++++++++++++
+ tests/test_idna.py | 13 +++++++++++++
+ 2 files changed, 27 insertions(+)
+
+diff --git a/idna/core.py b/idna/core.py
+index 0dae61a..a549326 100644
+--- a/idna/core.py
++++ b/idna/core.py
+@@ -340,6 +340,15 @@ def encode(s: Union[str, bytes, bytearray], strict: bool = False, uts46: bool =
+             raise IDNAError('should pass a unicode string to the function rather than a byte string.')
+     if uts46:
+         s = uts46_remap(s, std3_rules, transitional)
++
++    # Reject inputs that exceed the maximum DNS domain length up-front.
++    # Each codepoint in a U-label contributes at least one octet to its
++    # A-label form, so any input longer than the domain limit cannot
++    # produce a valid A-domain. Short-circuiting here prevents per-label
++    # validation from being driven into quadratic time
++    if len(s) > 254:
++        raise IDNAError("Domain too long")
++
+     trailing_dot = False
+     result = []
+     if strict:
+@@ -373,6 +382,11 @@ def decode(s: Union[str, bytes, bytearray], strict: bool = False, uts46: bool =
+         raise IDNAError('Invalid ASCII in A-label')
+     if uts46:
+         s = uts46_remap(s, std3_rules, False)
++    # See encode() for rationale; the same bound applies because every
++    # legal A-domain is at most 254 octets and every codepoint of a
++    # legal U-domain contributes at least one octet to its A-form.
++    if len(s) > 254:
++        raise IDNAError("Domain too long")
+     trailing_dot = False
+     result = []
+     if not strict:
+diff --git a/tests/test_idna.py b/tests/test_idna.py
+index 81afb32..5001b48 100755
+--- a/tests/test_idna.py
++++ b/tests/test_idna.py
+@@ -78,6 +78,19 @@ class IDNATests(unittest.TestCase):
+         self.assertFalse(idna.valid_label_length('a' * 64))
+         self.assertRaises(idna.IDNAError, idna.encode, 'a' * 64)
+ 
++    def test_oversized_input_rejected_promptly(self):
++        # GHSA-65pc-fj4g-8rjx: encode/decode must reject inputs that
++        # exceed the maximum DNS domain length before per-codepoint
++        # validation runs, so labels dominated by CONTEXTO codepoints
++        # cannot drive validation into quadratic time.
++        import time
++
++        for payload in ("٠" * 8000, "・" * 8000 + "漢"):
++            start = time.perf_counter()
++            self.assertRaises(idna.IDNAError, idna.encode, payload)
++            self.assertRaises(idna.IDNAError, idna.decode, payload)
++            self.assertLess(time.perf_counter() - start, 1.0)
++
+     def test_check_bidi(self):
+ 
+         l = '\u0061'