On Thu, 10 Sep 2026 03:05:12 -0700 Breno Leitao <[email protected]> wrote:
> On Thu, Sep 10, 2026 at 10:59:35AM +0900, Masami Hiramatsu (Google) wrote: > > From: Masami Hiramatsu (Google) <[email protected]> > > > > 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. > > > > Fixes: de462e5f1071 ("bootconfig: Fix to remove bootconfig data from initrd > > while boot") > > Cc: [email protected] > > Reported-by: Sashiko <[email protected]> > > Closes: > > https://lore.kernel.org/all/[email protected]/ > > Assisted-by: Antigravity:gemini-3.8-flash > > Signed-off-by: Masami Hiramatsu (Google) <[email protected]> > > Reviewed-by: Breno Leitao <[email protected]> Thanks! I'll make a small fix and send v4 with your reviewed-by. -- Masami Hiramatsu (Google) <[email protected]>
