[PATCH 2/2] glibc: Fix CVE-2026-5928

[Sourav Kumar Pramanik <UpStream_IP-SP@bmwtechworks.in>]

From: Sourav Kumar Pramanik <souravkumar.pramanik@bmwtechworks.in>

This change fixes CVE-2026-5928

Upstream-Status: Backport [https://sourceware.org/git/?p=glibc.git;a=commit;h=ef3bfb5f910011f3780cb06aa47e730035f53285]

Comment: Patch refreshed as per glibc 2.39 source code

Signed-off-by: Sourav Kumar Pramanik <souravkumar.pramanik@bmwtechworks.in>
---
 .../glibc/glibc/CVE-2026-5928.patch           | 105 ++++++++++++++++++
 meta/recipes-core/glibc/glibc_2.39.bb         |   1 +
 2 files changed, 106 insertions(+)
 create mode 100644 meta/recipes-core/glibc/glibc/CVE-2026-5928.patch

diff --git a/meta/recipes-core/glibc/glibc/CVE-2026-5928.patch b/meta/recipes-core/glibc/glibc/CVE-2026-5928.patch
new file mode 100644
index 0000000000..470ab1a1ec
--- /dev/null
+++ b/meta/recipes-core/glibc/glibc/CVE-2026-5928.patch
@@ -0,0 +1,105 @@
+From ef3bfb5f910011f3780cb06aa47e730035f53285 Mon Sep 17 00:00:00 2001
+From: Rocket Ma <marocketbd@gmail.com>
+Date: Fri, 1 May 2026 20:39:07 -0700
+Subject: [PATCH] libio: Fix ungetwc operating on byte stream [BZ #33998]
+
+* libio/wgenops.c: When _IO_wdefault_pbackfail attempts to push back one
+character, it accidently compare the wchar to push back with the last
+char from byte stream, instead of wide stream. Under specific coding,
+attacker may exploit this to leak information. This commit fix bug
+33998, or CVE-2026-5928.
+
+CVE: CVE-2026-5928
+Upstream-Status: Backport [https://sourceware.org/git/?p=glibc.git;a=commit;h=ef3bfb5f910011f3780cb06aa47e730035f53285]
+Comment: Patch refreshed as per glibc 2.39 source code
+
+Signed-off-by: Rocket Ma <marocketbd@gmail.com>
+Reviewed-by: Carlos O'Donell <carlos@redhat.com>
+Signed-off-by: Sourav Kumar Pramanik <souravkumar.pramanik@bmwtechworks.in>
+---
+ libio/Makefile              |  1 +
+ libio/bug-wgenops-bz33998.c | 54 +++++++++++++++++++++++++++++++++++++++++++++
+ libio/wgenops.c             |  4 ++--
+ 3 files changed, 57 insertions(+), 2 deletions(-)
+ create mode 100644 libio/bug-wgenops-bz33998.c
+
+diff --git a/libio/Makefile b/libio/Makefile
+--- a/libio/Makefile
++++ b/libio/Makefile
+@@ -83,6 +83,7 @@ tests = \
+   bug-ungetwc1 \
+   bug-ungetwc2 \
+   bug-wfflush \
++  bug-wgenops-bz33998 \
+   bug-wmemstream1 \
+   bug-wsetpos \
+   test-fmemopen \
+diff --git a/libio/bug-wgenops-bz33998.c b/libio/bug-wgenops-bz33998.c
+new file mode 100644
+--- /dev/null
++++ b/libio/bug-wgenops-bz33998.c
+@@ -0,0 +1,54 @@
++/* Regression test for ungetwc operating on byte stream (BZ #33998)
++   Copyright (C) 2026 The GNU Toolchain Authors.
++   This file is part of the GNU C Library.
++
++   The GNU C Library is free software; you can redistribute it and/or
++   modify it under the terms of the GNU Lesser General Public
++   License as published by the Free Software Foundation; either
++   version 2.1 of the License, or (at your option) any later version.
++
++   The GNU C Library is distributed in the hope that it will be useful,
++   but WITHOUT ANY WARRANTY; without even the implied warranty of
++   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
++   Lesser General Public License for more details.
++
++   You should have received a copy of the GNU Lesser General Public
++   License along with the GNU C Library; if not, see
++   <https://www.gnu.org/licenses/>.  */
++
++#include "support/temp_file.h"
++#include "support/xstdio.h"
++#include "support/xunistd.h"
++#include <stdlib.h>
++#include <unistd.h>
++#include <sys/mman.h>
++#include <stdio.h>
++#include <wchar.h>
++#include <support/check.h>
++
++static int
++do_test (void)
++{
++  char *filename;
++  int fd = create_temp_file ("tst-bz33998-", &filename);
++  TEST_VERIFY (fd != -1);
++  xwrite (fd, "A", sizeof ("A")); // write "A\0" by design
++  xclose (fd);
++
++  FILE *fp = xfopen (filename, "r+");
++  TEST_COMPARE (getwc (fp), L'A');
++  /* If the bug is fixed, then ungetwc should not touch byte stream.
++     If the bug is not fixed, ungetwc firstly match last read char, L'A',
++     failed, then the pbackfail branch, matching last read char in byte
++     stream, that is, '\0' (initialized when setup wide stream). */
++  char *old_read_ptr = fp->_IO_read_ptr;
++  TEST_COMPARE (ungetwc (L'\0', fp), L'\0');
++  TEST_VERIFY (fp->_IO_read_ptr == old_read_ptr);
++
++  xfclose (fp);
++  free (filename);
++
++  return 0;
++}
++
++#include <support/test-driver.c>
+diff --git a/libio/wgenops.c b/libio/wgenops.c
+--- a/libio/wgenops.c
++++ b/libio/wgenops.c
+@@ -111,2 +111,2 @@ _IO_wdefault_pbackfail (FILE *fp, wint_t c)
+-      && (wint_t) fp->_IO_read_ptr[-1] == c)
+-    --fp->_IO_read_ptr;
++      && (wint_t) fp->_wide_data->_IO_read_ptr[-1] == c)
++    --fp->_wide_data->_IO_read_ptr;
+-- 
+2.43.7
diff --git a/meta/recipes-core/glibc/glibc_2.39.bb b/meta/recipes-core/glibc/glibc_2.39.bb
index b01225e530..74db1ac507 100644
--- a/meta/recipes-core/glibc/glibc_2.39.bb
+++ b/meta/recipes-core/glibc/glibc_2.39.bb
@@ -58,6 +58,7 @@ SRC_URI =  "${GLIBC_GIT_URI};branch=${SRCBRANCH};name=glibc \
            file://0001-stdlib-Add-single-threaded-fast-path-to-rand.patch \
            file://0024-CVE-2026-5435.patch \
            file://CVE-2026-5450.patch \
+           file://CVE-2026-5928.patch \
 "
 S = "${WORKDIR}/git"
 B = "${WORKDIR}/build-${TARGET_SYS}"
-- 
2.43.0