linux-kernel - Re: [PATCH 1/2] initramfs: Check negative timestamp to prevent broken cpio archive

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Message-ID: <CAK7LNAR8g246Zvy78mEFN5c_NLWSMNajF52tPLbtkLuiY_Xn7A@mail.gmail.com>
Date:   Sun, 16 Apr 2023 17:46:24 +0900
From:   Masahiro Yamada <masahiroy@...nel.org>
To:     Benjamin Gray <bgray@...ux.ibm.com>
Cc:     linux-kernel@...r.kernel.org, linux-kbuild@...r.kernel.org
Subject: Re: [PATCH 1/2] initramfs: Check negative timestamp to prevent broken
 cpio archive

On Mon, Mar 20, 2023 at 1:09 PM Benjamin Gray <bgray@...ux.ibm.com> wrote:
>
> Similar to commit 4c9d410f32b3 ("initramfs: Check timestamp to prevent
> broken cpio archive"), except asserts that the timestamp is
> non-negative. This can happen when the KBUILD_BUILD_TIMESTAMP is a value
> before UNIX epoch, which may be set when making reproducible builds that
> don't want to look like they use a valid date.
>
> While support for dates before 1970 might not be supported, this is more
> about preventing undetected CPIO corruption. The printf's use a minimum
> length format specifier, and will happily make the field longer than 8
> characters if they need to.
>
> Signed-off-by: Benjamin Gray <bgray@...ux.ibm.com>
>
> ---

Applied to linux-kbuild.   (only 1/2)
Thanks.




>
> Ran into this when setting KBUILD_BUILD_TIMESTAMP=0000-01-01. The kernel
> builds and boots to an initramfs just fine, but inexplicably failed to
> load any root disks. It was a pain to debug, because the first sign of
> an issue was so deep into the boot sequence.
> ---
>  usr/gen_init_cpio.c | 12 +++++++++---
>  1 file changed, 9 insertions(+), 3 deletions(-)
>
> diff --git a/usr/gen_init_cpio.c b/usr/gen_init_cpio.c
> index ee01e40e8bc6..61230532fef1 100644
> --- a/usr/gen_init_cpio.c
> +++ b/usr/gen_init_cpio.c
> @@ -353,6 +353,12 @@ static int cpio_mkfile(const char *name, const char *location,
>                 buf.st_mtime = 0xffffffff;
>         }
>
> +       if (buf.st_mtime < 0) {
> +               fprintf(stderr, "%s: Timestamp negative, clipping.\n",
> +                       location);
> +               buf.st_mtime = 0;
> +       }
> +
>         if (buf.st_size > 0xffffffff) {
>                 fprintf(stderr, "%s: Size exceeds maximum cpio file size\n",
>                         location);
> @@ -602,10 +608,10 @@ int main (int argc, char *argv[])
>         /*
>          * Timestamps after 2106-02-07 06:28:15 UTC have an ascii hex time_t
>          * representation that exceeds 8 chars and breaks the cpio header
> -        * specification.
> +        * specification. Negative timestamps similarly exceed 8 chars.
>          */
> -       if (default_mtime > 0xffffffff) {
> -               fprintf(stderr, "ERROR: Timestamp too large for cpio format\n");
> +       if (default_mtime > 0xffffffff || default_mtime < 0) {
> +               fprintf(stderr, "ERROR: Timestamp out of range for cpio format\n");
>                 exit(1);
>         }
>
>
> base-commit: 065ffaee73892e8a3629b4cfbe635697807a3c6f
> --
> 2.39.2
>


-- 
Best Regards
Masahiro Yamada