+ bootconfig-fix-integer-overflow-in-initrd-size-check.patch added to mm-nonmm-unstable branch

[Andrew Morton <akpm@linux-foundation.org>]

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The patch titled
     Subject: bootconfig: fix integer overflow in initrd size check
has been added to the -mm mm-nonmm-unstable branch.  Its filename is
     bootconfig-fix-integer-overflow-in-initrd-size-check.patch

This patch will shortly appear at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/bootconfig-fix-integer-overflow-in-initrd-size-check.patch

This patch will later appear in the mm-nonmm-unstable branch at
    git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

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------------------------------------------------------
From: Masami Hiramatsu (Google) <mhiramat@kernel.org>
Subject: bootconfig: fix integer overflow in initrd size check
Date: Fri, 11 Sep 2026 00:15:34 +0900

Sashiko reported that in get_boot_config_from_initrd(), a crafted initrd
with a huge bootconfig size (such as 0xFFFFFFFF) can cause the pointer
arithmetic:

    data = ((void *)hdr) - size;

to wrap around on 32-bit systems (or when pointer subtraction overflows). 
Because data wraps around, the subsequent bounds check:

    if ((unsigned long)data < initrd_start)

evaluates to false, bypassing the check.  The kernel then calls
xbc_calc_checksum(data, size), which attempts to read 4GB of memory,
hitting unmapped pages and triggering a fatal kernel page fault during
early boot.  Furthermore, on 64-bit systems with an initrd > 4.29 GB, an
unbounded 32-bit size can similarly bypass the initrd_start check.

Fix this by:
1. Ensuring the initrd is at least large enough to contain the bootconfig
   footer and verifying hdr is within the initrd bounds.
2. Checking that size does not exceed XBC_DATA_MAX and does not exceed
   the available space between initrd_start and hdr before performing
   pointer subtraction.

Link: https://lore.kernel.org/178905333479.213925.1358412668943562406.stgit@devnote2
Fixes: de462e5f1071 ("bootconfig: Fix to remove bootconfig data from initrd while boot")
Signed-off-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
Reported-by: Sashiko <sashiko-bot@kernel.org>
Closes: https://lore.kernel.org/all/20260910010137.EE0431F000FF@smtp.kernel.org/
Assisted-by: Antigravity:gemini-3.8-flash
Cc: Breno Leitao <leitao@debian.org>
Cc: Christian Brauner <brauner@kernel.org>
Cc: Doug Anderson <dianders@chromium.org>
Cc: Huacai Chen <chenhuacai@kernel.org>
Cc: Marc Rutland <mark.rutland@arm.com>
Cc: Ryan Roberts <ryan.roberts@arm.com>
Cc: Sang-Heon Jeon <ekffu200098@gmail.com>
Cc: Thomas Weißschuh <thomas.weissschuh@linutronix.de>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 init/main.c |   25 +++++++++++++++----------
 1 file changed, 15 insertions(+), 10 deletions(-)

--- a/init/main.c~bootconfig-fix-integer-overflow-in-initrd-size-check
+++ a/init/main.c
@@ -277,7 +277,8 @@ static void * __init get_boot_config_fro
 	u8 *hdr;
 	int i;
 
-	if (!initrd_end)
+	if (!initrd_end || initrd_end < initrd_start ||
+	    initrd_end - initrd_start < BOOTCONFIG_MAGIC_LEN + 8)
 		return NULL;
 
 	data = (char *)initrd_end - BOOTCONFIG_MAGIC_LEN;
@@ -294,16 +295,26 @@ static void * __init get_boot_config_fro
 
 found:
 	hdr = (u8 *)(data - 8);
+	if ((unsigned long)hdr < initrd_start)
+		return NULL;
+
 	size = get_unaligned_le32(hdr);
 	csum = get_unaligned_le32(hdr + 4);
 
-	data = ((void *)hdr) - size;
-	if ((unsigned long)data < initrd_start) {
-		pr_err("bootconfig size %d is greater than initrd size %ld\n",
+	if (size > XBC_DATA_MAX) {
+		pr_err("bootconfig size %u is greater than max size %d\n",
+			size, XBC_DATA_MAX);
+		return NULL;
+	}
+
+	if (size > ((unsigned long)hdr - initrd_start)) {
+		pr_err("bootconfig size %u is greater than initrd size %lu\n",
 			size, initrd_end - initrd_start);
 		return NULL;
 	}
 
+	data = ((void *)hdr) - size;
+
 	if (xbc_calc_checksum(data, size) != csum) {
 		pr_err("bootconfig checksum failed\n");
 		return NULL;
@@ -394,12 +405,6 @@ static void __init setup_boot_config(voi
 		return;
 	}
 
-	if (size >= XBC_DATA_MAX) {
-		pr_err("bootconfig size %ld greater than max size %d\n",
-			(long)size, XBC_DATA_MAX);
-		return;
-	}
-
 	ret = xbc_init(data, size, &msg, &pos);
 	if (ret < 0) {
 		if (pos < 0)
_

Patches currently in -mm which might be from mhiramat@kernel.org are

bootconfig-reject-unexpected-data-after-null-character.patch
tools-bootconfig-consolidate-xbc_init-to-error-message-wrapper.patch
bootconfig-skip-internal-tree-sanity-checks-in-kernel.patch
tools-bootconfig-fix-integer-overflow-and-truncation-in-size-checks.patch
bootconfig-fix-integer-overflow-in-initrd-size-check.patch