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

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

[Andrew Morton]

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

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

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

Before you just go and hit "reply", please:
   a) Consider who else should be cc'ed
   b) Prefer to cc a suitable mailing list as well
   c) Ideally: find the original patch on the mailing list and do a
      reply-to-all to that, adding suitable additional cc's

*** Remember to use Documentation/process/submit-checklist.rst when testing your code ***

The -mm tree is included into linux-next via various
branches at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
and is updated there most days

------------------------------------------------------
From: Masami Hiramatsu (Google) <mhiramat@kernel.org>
Subject: tools/bootconfig: Fix integer overflow in size check
Date: Thu, 10 Sep 2026 09:30:46 +0900

Sashiko reported that on 32-bit systems, if the size in the bootconfig
footer is corrupted such that adding BOOTCONFIG_FOOTER_SIZE wraps around
(for instance, if size is 0xFFFFFFFF), the size check in
load_xbc_from_initrd() can be bypassed:

    if (stat.st_size < size + BOOTCONFIG_FOOTER_SIZE) {
        pr_err("bootconfig size is too big\n");
        return -E2BIG;
    }

This would lead to load_xbc_fd() being called with a negative size,
resulting in an undersized allocation, heap overflow on read, and
out-of-bounds write on the terminating null byte.

Avoid the integer overflow by checking whether size is greater than
stat.st_size - BOOTCONFIG_FOOTER_SIZE.  Since stat.st_size is already
verified to be at least BOOTCONFIG_FOOTER_SIZE earlier in the function,
this subtraction will never underflow.

Link: https://lore.kernel.org/178900024679.183840.10345859264677533824.stgit@devnote2
Fixes: 950313ebf79c ("tools: bootconfig: Add bootconfig command")
Signed-off-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
Reported-by: Sashiko <sashiko-bot@kernel.org>
Closes: https://lore.kernel.org/all/20260909161113.16C691F00A3A@smtp.kernel.org/
Assisted-by: Antigravity:gemini-3.8-flash
Cc: Sang-Heon Jeon <ekffu200098@gmail.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 tools/bootconfig/main.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/tools/bootconfig/main.c~tools-bootconfig-fix-integer-overflow-in-size-check
+++ a/tools/bootconfig/main.c
@@ -218,7 +218,7 @@ static int load_xbc_from_initrd(int fd,
 	csum = le32toh(csum);
 
 	/* Wrong size error  */
-	if (stat.st_size < size + BOOTCONFIG_FOOTER_SIZE) {
+	if (size > stat.st_size - BOOTCONFIG_FOOTER_SIZE) {
 		pr_err("bootconfig size is too big\n");
 		return -E2BIG;
 	}
_

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

tools-bootconfig-fix-integer-overflow-in-size-check.patch
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-in-size-check.patch added to mm-hotfixes-unstable branch

[Andrew Morton]

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

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

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

Before you just go and hit "reply", please:
   a) Consider who else should be cc'ed
   b) Prefer to cc a suitable mailing list as well
   c) Ideally: find the original patch on the mailing list and do a
      reply-to-all to that, adding suitable additional cc's

*** Remember to use Documentation/process/submit-checklist.rst when testing your code ***

The -mm tree is included into linux-next via various
branches at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
and is updated there most days

------------------------------------------------------
From: Masami Hiramatsu (Google) <mhiramat@kernel.org>
Subject: tools/bootconfig: fix integer overflow in size check
Date: Thu, 10 Sep 2026 09:45:45 +0900

Sashiko reported that on 32-bit systems, if an attacker crafts size in the
bootconfig footer such that adding BOOTCONFIG_FOOTER_SIZE wraps around
(for instance, if size is 0xFFFFFFFF), the size check in
load_xbc_from_initrd() can be bypassed:

    if (stat.st_size < size + BOOTCONFIG_FOOTER_SIZE) {
        pr_err("bootconfig size is too big\n");
        return -E2BIG;
    }

This would lead to load_xbc_fd() being called with a negative size,
resulting in an undersized allocation, heap overflow on read, and
out-of-bounds write on the terminating null byte.

Avoid the integer overflow by checking whether size is greater than
stat.st_size - BOOTCONFIG_FOOTER_SIZE.  Since stat.st_size is already
verified to be at least BOOTCONFIG_FOOTER_SIZE earlier in the function,
this subtraction will never underflow.

Also reject size > XBC_DATA_MAX upfront in load_xbc_from_initrd() to avoid
allocating and reading oversized configurations into memory before
xbc_init() validation.

Link: https://lore.kernel.org/178900114498.187028.9558747732041210116.stgit@devnote2
Fixes: 950313ebf79c ("tools: bootconfig: Add bootconfig command")
Signed-off-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
Reported-by: Sashiko <sashiko-bot@kernel.org>
Closes: https://lore.kernel.org/all/20260909161113.16C691F00A3A@smtp.kernel.org/
Assisted-by: Antigravity:gemini-3.8-flash
Cc: Sang-Heon Jeon <ekffu200098@gmail.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 tools/bootconfig/main.c |    3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

--- a/tools/bootconfig/main.c~tools-bootconfig-fix-integer-overflow-in-size-check
+++ a/tools/bootconfig/main.c
@@ -218,7 +218,8 @@ static int load_xbc_from_initrd(int fd,
 	csum = le32toh(csum);
 
 	/* Wrong size error  */
-	if (stat.st_size < size + BOOTCONFIG_FOOTER_SIZE) {
+	if (size > XBC_DATA_MAX ||
+	    size > stat.st_size - BOOTCONFIG_FOOTER_SIZE) {
 		pr_err("bootconfig size is too big\n");
 		return -E2BIG;
 	}
_

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

tools-bootconfig-fix-integer-overflow-in-size-check.patch
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