Re: [PATCH v3 2/2] bootconfig: Fix integer overflow in initrd size check

On Thu, 10 Sep 2026 02:09:01 +0000
sashiko-bot@kernel.org wrote:

Thank you for your contribution! Sashiko AI review found 2 potential issue(s) to consider:
- [Medium] Mismatched boundary checks for XBC_DATA_MAX cause inconsistent fallback behavior for embedded bootconfigs.
- [Low] Misleading error message when bootconfig size exceeds XBC_DATA_MAX.
--

commit a24325c6fe0374f1cfc3fc8cbe63efbad0f22f32
Author: Masami Hiramatsu (Google) [off-list ref]

bootconfig: Fix integer overflow in initrd size check

This commit fixes an integer overflow where a crafted initrd with a huge
bootconfig size can cause pointer arithmetic wrap-around. It ensures the
initrd bounds are respected and verifies the size does not exceed max limits.

Closes: https://lore.kernel.org/all/20260910010137.EE0431F000FF@smtp.kernel.org/ (local)

quoted

diff --git a/init/main.c b/init/main.c
index a9362b2cc258a..de24c41ce815e 100644
--- a/init/main.c
+++ b/init/main.c

[ ... ]

quoted

@@ -294,16 +295,21 @@ 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 ||

[Severity: Medium]
If the size is exactly equal to XBC_DATA_MAX, this check passes and the
function returns a valid data pointer. This prevents the caller from falling
back to the embedded bootconfig:

init/main.c:setup_boot_config() {
	...
	data = get_boot_config_from_initrd(&size);
	if (!data) {
		data = xbc_get_embedded_bootconfig(&size);
		...
	}
	...
}

However, setup_boot_config() uses inclusive inequality for XBC_DATA_MAX:

init/main.c:setup_boot_config() {
	...
	if (size >= XBC_DATA_MAX) {
		pr_err("bootconfig size %ld greater than max size %d\n", ...);
		return;
	}
	...
}

Hmm, this is wrong. Since XBC_DATA_MAX is including maximum size, 
setup_boot_config() should change this condition.

Because the limits don't match, an exact size of XBC_DATA_MAX causes
setup_boot_config() to reject the payload and abort without attempting
the fallback. Should this check use size >= XBC_DATA_MAX to match?

quoted

+	    size > ((unsigned long)hdr - initrd_start)) {
+		pr_err("bootconfig size %u is greater than initrd size %lu\n",
+			size, initrd_end - initrd_start);

[Severity: Low]
If this error path is taken specifically because size > XBC_DATA_MAX, the
error message claims the bootconfig size is greater than the initrd size.
Can this message be updated to accurately reflect which limit was exceeded?

Ah, good catch :)

Thanks,

quoted

 		return NULL;
 	}
 
+	data = ((void *)hdr) - size;
+
 	if (xbc_calc_checksum(data, size) != csum) {
 		pr_err("bootconfig checksum failed\n");
 		return NULL;

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/178900555453.200943.4719889510443114485.stgit@devnote2?part=2

-- 
Masami Hiramatsu (Google) [off-list ref]