Re: [OE-core] [scarthgap][PATCHv2 1/2] glibc: Fix CVE-2026-5450

["Yoann Congal" <yoann.congal@smile.fr>]

Hello,

On Mon Oct 5, 2026 at 7:56 AM CEST, Sourav Kumar Pramanik via lists.openembedded.org wrote:
> From: Sourav Kumar Pramanik <souravkumar.pramanik@bmwtechworks.in>
>
> This change fixes CVE-2026-5450

Why? Please explain why you think this patch does fix this CVE (Usually
it comes from NVD data)

>
> Upstream-Status: Backport [https://sourceware.org/cgit/glibc/commit/?id=839898777226a3ed88c0859f25ffe712519b4ead]
^ This line is only useful in the patch file itself, not in the commit
message.

>
> Comment: Patch refreshed as per glibc 2.39 source code
Sorry but this comment states the obviously and does not provide
information about what was modified during the refresh.

>
> Signed-off-by: Sourav Kumar Pramanik <souravkumar.pramanik@bmwtechworks.in>
> ---
>  .../glibc/glibc/CVE-2026-5450.patch           | 113 ++++++++++++++++++
>  meta/recipes-core/glibc/glibc_2.39.bb         |   1 +
>  2 files changed, 114 insertions(+)
>  create mode 100644 meta/recipes-core/glibc/glibc/CVE-2026-5450.patch
>
> diff --git a/meta/recipes-core/glibc/glibc/CVE-2026-5450.patch b/meta/recipes-core/glibc/glibc/CVE-2026-5450.patch
> new file mode 100644
> index 0000000000..adea5c3f01
> --- /dev/null
> +++ b/meta/recipes-core/glibc/glibc/CVE-2026-5450.patch
> @@ -0,0 +1,113 @@
> +From 839898777226a3ed88c0859f25ffe712519b4ead Mon Sep 17 00:00:00 2001
> +From: Rocket Ma <marocketbd@gmail.com>
> +Date: Fri, 17 Apr 2026 23:48:41 -0700
> +Subject: [PATCH] stdio-common: Fix buffer overflow in scanf %mc [BZ #34008]
> +
> +* stdio-common/vfscanf-internal.c: When enlarging allocated buffer with
> +format %mc or %mC, glibc allocates one byte less, leading to
> +user-controlled one byte overflow. This commit fixes BZ #34008, or
> +CVE-2026-5450.
> +
> +CVE: CVE-2026-5450
> +Upstream-Status: Backport [https://sourceware.org/cgit/glibc/commit/?id=839898777226a3ed88c0859f25ffe712519b4ead]
> +Comment: Patch refreshed as per glibc 2.39 source code

(See above about "Comment:")


> +
> +Reviewed-by: Carlos O'Donell <carlos@redhat.com>
> +Signed-off-by: Rocket Ma <marocketbd@gmail.com>
> +Reviewed-by: H.J. Lu <hjl.tools@gmail.com>
> +Signed-off-by: Sourav Kumar Pramanik <souravkumar.pramanik@bmwtechworks.in>
> +---
> + stdio-common/Makefile              |  4 ++++
> + stdio-common/tst-vfscanf-bz34008.c | 48 +++++++++++++++++++++++++++++++++++++
> + stdio-common/vfscanf-internal.c    |  6 +++---
> + 3 files changed, 55 insertions(+), 3 deletions(-)
> + create mode 100644 stdio-common/tst-vfscanf-bz34008.c
> +
> +diff --git a/stdio-common/Makefile b/stdio-common/Makefile
> +--- a/stdio-common/Makefile
> ++++ b/stdio-common/Makefile
> +@@ -266,6 +266,7 @@ tests := \
> +   tst-vfprintf-width-i18n \
> +   tst-vfprintf-width-prec \
> +   tst-vfprintf-width-prec-alloc \
> ++  tst-vfscanf-bz34008 \
> +   tst-wc-printf \
> +   tstdiomisc \
> +   tstgetln \
> +@@ -401,6 +402,9 @@ tst-printf-bz18872-ENV = MALLOC_TRACE=$(objpfx)tst-printf-bz18872.mtrace \
> + tst-vfprintf-width-prec-ENV = \
> +   MALLOC_TRACE=$(objpfx)tst-vfprintf-width-prec.mtrace \
> +   LD_PRELOAD=$(common-objpfx)/malloc/libc_malloc_debug.so
> ++tst-vfscanf-bz34008-ENV = \
> ++  MALLOC_CHECK_=3 \
> ++  LD_PRELOAD=$(common-objpfx)/malloc/libc_malloc_debug.so
> + tst-printf-bz25691-ENV = \
> +   MALLOC_TRACE=$(objpfx)tst-printf-bz25691.mtrace \
> +   LD_PRELOAD=$(common-objpfx)/malloc/libc_malloc_debug.so
> +diff --git a/stdio-common/tst-vfscanf-bz34008.c b/stdio-common/tst-vfscanf-bz34008.c
> +new file mode 100644
> +--- /dev/null
> ++++ b/stdio-common/tst-vfscanf-bz34008.c
> +@@ -0,0 +1,48 @@
> ++/* Regression test for vfscanf %Nmc out-of-bound write (BZ #34008)
> ++   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 "malloc/mcheck.h"
> ++#include <stddef.h>
> ++#include <stdio.h>
> ++#include <string.h>
> ++#include <wchar.h>
> ++#include <stdlib.h>
> ++#include <malloc.h>
> ++#include <support/check.h>
> ++
> ++#define WIDTH 0x410
> ++#define SCANFSTR "%1040mc"
> ++static int
> ++do_test (void)
> ++{
> ++  mcheck_pedantic (NULL);
> ++  char *input = malloc (WIDTH + 1);
> ++  TEST_VERIFY (input != NULL);
> ++  memset (input, 'A', WIDTH);
> ++  input[WIDTH] = '\0';
> ++
> ++  char *buf = NULL;
> ++  TEST_VERIFY (sscanf (input, SCANFSTR, &buf) != -1);
> ++  TEST_VERIFY (buf != NULL);
> ++
> ++  free (buf);
> ++  free (input);
> ++  return 0;
> ++}
> ++
> ++#include <support/test-driver.c>
> +diff --git a/stdio-common/vfscanf-internal.c b/stdio-common/vfscanf-internal.c
> +--- a/stdio-common/vfscanf-internal.c
> ++++ b/stdio-common/vfscanf-internal.c
> +@@ -857 +857 @@ __vfscanf_internal (FILE *s, const char *format, va_list argptr,
> +-			      + (strsize >= width ? width - 1 : strsize);
> ++			      + (strsize >= width ? width : strsize);
> +@@ -928 +928 @@ __vfscanf_internal (FILE *s, const char *format, va_list argptr,
> +-			= strsize + (strsize > width ? width - 1 : strsize);
> ++			= strsize + (strsize >= width ? width : strsize);
> +@@ -983 +983 @@ __vfscanf_internal (FILE *s, const char *format, va_list argptr,
> +-		      = strsize + (strsize > width ? width - 1 : strsize);
> ++		      = strsize + (strsize >= width ? width : strsize);

The above 3 hunks have no context which greatly increase the chances of
a badly applied patch.

Can you send a v3 with the usual "3 lines of context"?

> +-- 
> +2.43.7
> diff --git a/meta/recipes-core/glibc/glibc_2.39.bb b/meta/recipes-core/glibc/glibc_2.39.bb
> index 88ad5e44e8..b01225e530 100644
> --- a/meta/recipes-core/glibc/glibc_2.39.bb
> +++ b/meta/recipes-core/glibc/glibc_2.39.bb
> @@ -57,6 +57,7 @@ SRC_URI =  "${GLIBC_GIT_URI};branch=${SRCBRANCH};name=glibc \
>             file://0023-qemu-stale-process.patch \
>             file://0001-stdlib-Add-single-threaded-fast-path-to-rand.patch \
>             file://0024-CVE-2026-5435.patch \
> +           file://CVE-2026-5450.patch \
>  "
>  S = "${WORKDIR}/git"
>  B = "${WORKDIR}/build-${TARGET_SYS}"

Thanks!
-- 
Yoann Congal
Smile ECS