FAILED: patch "[PATCH] bootconfig: Fix integer overflow in initrd size check" failed to apply to 6.18-stable tree

The patch below does not apply to the 6.18-stable tree.
If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to <[email protected]>.

To reproduce the conflict and resubmit, you may use the following commands:

git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-6.18.y
git checkout FETCH_HEAD
git cherry-pick -x 7812d6dab0698001e50e8c2f901e17da3eb6f429
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<[email protected]>' --in-reply-to '2026091615-curry-barracuda-b99e@gregkh' --subject-prefix 'PATCH 6.18.y' 'HEAD^..'

Possible dependencies:

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From 7812d6dab0698001e50e8c2f901e17da3eb6f429 Mon Sep 17 00:00:00 2001
From: "Masami Hiramatsu (Google)" <[email protected]>
Date: Fri, 11 Sep 2026 00:15:34 +0900
Subject: [PATCH] bootconfig: Fix integer overflow in initrd size check

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.

index 2613d3f9b3ce..16749bb7a219 100644
@@ -277,7 +277,8 @@ static void * __init get_boot_config_from_initrd(size_t *_size)
 	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_from_initrd(size_t *_size)
 
 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(void)
 		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)

From: Sun Jian <[email protected]>

[ Upstream commit 499f86de4f8c34e19a57daf2b6f0cba848e91994 ]

get_boot_config_from_initrd() scans up to 3 bytes before initrd_end to handle GRUB 4-byte alignment. As a result, the bootconfig header immediately preceding the magic may be unaligned.

Read the size and checksum fields with get_unaligned_le32() instead of casting to u32 * and using le32_to_cpu(), avoiding potential unaligned access and silencing sparse "cast to restricted __le32" warnings.

Sparse warnings (gcc + C=1):
init/main.c:292:16: warning: cast to restricted __le32 init/main.c:293:16: warning: cast to restricted __le32

No functional change intended.

Stable-dep-of: 7812d6dab069 ("bootconfig: Fix integer overflow in initrd size check")

---
 init/main.c | 9 +++++----
 1 file changed, 5 insertions(+), 4 deletions(-)

index e3ef1eb34aa3e..b254678062c72 100644
@@ -104,6 +104,7 @@
 #include <linux/pidfs.h>
 #include <linux/ptdump.h>
 #include <linux/time_namespace.h>
+#include <linux/unaligned.h>
 #include <net/net_namespace.h>
 
 #include <asm/io.h>

@@ -269,7 +270,7 @@ static void * __init get_boot_config_from_initrd(size_t *_size)
 {
 	u32 size, csum;
 	char *data;
-	u32 *hdr;
+	u8 *hdr;
 	int i;
 
 	if (!initrd_end)

@@ -288,9 +289,9 @@ static void * __init get_boot_config_from_initrd(size_t *_size)
 	return NULL;
 
 found:
-	hdr = (u32 *)(data - 8);
-	size = le32_to_cpu(hdr[0]);
-	csum = le32_to_cpu(hdr[1]);
+	hdr = (u8 *)(data - 8);
+	size = get_unaligned_le32(hdr);
+	csum = get_unaligned_le32(hdr + 4);
 
 	data = ((void *)hdr) - size;
 	if ((unsigned long)data < initrd_start) {

2.53.0

From: "Masami Hiramatsu (Google)" <[email protected]>

[ Upstream commit 7812d6dab0698001e50e8c2f901e17da3eb6f429 ]

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.

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

index b254678062c72..a9f04c8caf7ec 100644
@@ -273,7 +273,8 @@ static void * __init get_boot_config_from_initrd(size_t *_size)
 	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;

@@ -290,16 +291,26 @@ static void * __init get_boot_config_from_initrd(size_t *_size)
 
 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;

@@ -402,12 +413,6 @@ static void __init setup_boot_config(void)
 		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)

2.53.0