xz: Fix CVE-2026-34743

Pick patch from [1] as 5.4.x upstream backport of [2] mentioned in Debian report in [3].

[1] 8538443d08
[2] c8c22869e7
[3] https://security-tracker.debian.org/tracker/CVE-2026-34743

(From OE-Core rev: 3e239f3c7ff23694741c65cf8444215e3659d690)

Signed-off-by: Hugo SIMELIERE (Schneider Electric) <hsimeliere.opensource@witekio.com>
Reviewed-by: Bruno VERNAY <bruno.vernay@se.com>
Signed-off-by: Jeremy Rosen <jeremy.rosen@smile.fr>
Signed-off-by: Paul Barker <paul@pbarker.dev>

meta/recipes-extended/xz/xz/CVE-2026-34743.patch

@@ -0,0 +1,68 @@
+From ae7abca7c721c73bb4aadf41a82a720a842a4364 Mon Sep 17 00:00:00 2001
+From: Lasse Collin <lasse.collin@tukaani.org>
+Date: Sun, 29 Mar 2026 19:11:21 +0300
+Subject: [PATCH] liblzma: Fix a buffer overflow in lzma_index_append()
+
+If lzma_index_decoder() was used to decode an Index that contained no
+Records, the resulting lzma_index had an invalid internal "prealloc"
+value. If lzma_index_append() was called on this lzma_index, too
+little memory would be allocated and a buffer overflow would occur.
+
+While this combination of the API functions is meant to work, in the
+real-world apps this call sequence is rare or might not exist at all.
+
+This bug is older than xz 5.0.0, so all stable releases are affected.
+
+CVE: CVE-2026-34743
+Upstream-Status: Backport [https://github.com/tukaani-project/xz/commit/8538443d08591693a8c61f3a03656650f39c7c32]
+
+Reported-by: GitHub user christos-spearbit
+(cherry picked from commit c8c22869e780ff57c96b46939c3d79ff99395f87)
+(cherry picked from commit 8538443d08591693a8c61f3a03656650f39c7c32)
+Signed-off-by: Hugo SIMELIERE (Schneider Electric) <hsimeliere.opensource@witekio.com>
+---
+ src/liblzma/common/index.c | 21 +++++++++++++++++++++
+ 1 file changed, 21 insertions(+)
+
+diff --git a/src/liblzma/common/index.c b/src/liblzma/common/index.c
+index 8a35f439..dae7cab5 100644
+--- a/src/liblzma/common/index.c
++++ b/src/liblzma/common/index.c
+@@ -434,6 +434,26 @@ lzma_index_prealloc(lzma_index *i, lzma_vli records)
+ 	if (records > PREALLOC_MAX)
+ 		records = PREALLOC_MAX;
+ 
++	// If index_decoder.c calls us with records == 0, it's decoding
++	// an Index that has no Records. In that case the decoder won't call
++	// lzma_index_append() at all, and i->prealloc isn't used during
++	// the Index decoding either.
++	//
++	// Normally the first lzma_index_append() call from the Index decoder
++	// would reset i->prealloc to INDEX_GROUP_SIZE. With no Records,
++	// lzma_index_append() isn't called and the resetting of prealloc
++	// won't occur either. Thus, if records == 0, use the default value
++	// INDEX_GROUP_SIZE instead.
++	//
++	// NOTE: lzma_index_append() assumes i->prealloc > 0. liblzma <= 5.8.2
++	// didn't have this check and could set i->prealloc = 0, which would
++	// result in a buffer overflow if the application called
++	// lzma_index_append() after decoding an empty Index. Appending
++	// Records after decoding an Index is a rare thing to do, but
++	// it is supposed to work.
++	if (records == 0)
++		records = INDEX_GROUP_SIZE;
++
+ 	i->prealloc = (size_t)(records);
+ 	return;
+ }
+@@ -686,6 +706,7 @@ lzma_index_append(lzma_index *i, const lzma_allocator *allocator,
+ 		++g->last;
+ 	} else {
+ 		// We need to allocate a new group.
++		assert(i->prealloc > 0);
+ 		g = lzma_alloc(sizeof(index_group)
+ 				+ i->prealloc * sizeof(index_record),
+ 				allocator);
+-- 
+2.43.0
+

meta/recipes-extended/xz/xz_5.4.7.bb

@@ -30,6 +30,7 @@ SRC_URI = "https://github.com/tukaani-project/xz/releases/download/v${PV}/xz-${P
            file://CVE-2025-31115-02.patch \
            file://CVE-2025-31115-03.patch \
            file://CVE-2025-31115-04.patch \
+           file://CVE-2026-34743.patch \
           "
 SRC_URI[sha256sum] = "8db6664c48ca07908b92baedcfe7f3ba23f49ef2476864518ab5db6723836e71"
 UPSTREAM_CHECK_REGEX = "releases/tag/v(?P<pver>\d+(\.\d+)+)"