On Tue 12 Oct 2021 18:52:34 GMT Nicolas Schier wrote:
> Cpio format reserves 8 bytes for an ASCII representation of a time_t
> timestamp.
> While 2106-02-07 06:28:15 UTC (time_t = 0xffffffff) is still some years in the
> future, a poorly chosen date string for KBUILD_BUILD_TIMESTAMP, converted into
> seconds since the epoch, might lead to exceeded cpio timestamp limits that
> result in a broken cpio archive. Add timestamp checks to prevent overrun of
> the 8-byte cpio header field.
>
> My colleague Thomas Kühnel discovered the behaviour, when we accidentally fed
> SOURCE_DATE_EPOCH to KBUILD_BUILD_TIMESTAMP as is: some timestamps (e.g.
> 1607420928 = 2021-12-08 10:48:48) will be interpreted by `date` as a valid date
> specification of science fictional times (here: year 160742). Even though this
> is bad input for KBUILD_BUILD_TIMESTAMP, it should not break the initramfs
> cpio format.
>
> Signed-off-by: Nicolas Schier <nicolas@xxxxxxxxx>
> Cc: Thomas Kühnel <thomas.kuehnel@xxxxxx>
> ---
> usr/gen_init_cpio.c | 17 +++++++++++++++++
> 1 file changed, 17 insertions(+)
>
> --
> Changes v1 to v2:
> * add timezone name (UTC) to specific time stamps
> * fix typo: results -> result
>
> diff --git a/usr/gen_init_cpio.c b/usr/gen_init_cpio.c
> index 03b21189d58b..584ea45cff70 100644
> --- a/usr/gen_init_cpio.c
> +++ b/usr/gen_init_cpio.c
> @@ -320,6 +320,12 @@ static int cpio_mkfile(const char *name, const char *location,
> goto error;
> }
>
> + if (buf.st_mtime > 0xffffffff) {
> + fprintf(stderr, "%s: Timestamp exceeds maximum cpio timestamp, clipping.\n",
> + location);
> + buf.st_mtime = 0xffffffff;
> + }
> +
> filebuf = malloc(buf.st_size);
> if (!filebuf) {
> fprintf (stderr, "out of memory\n");
> @@ -551,6 +557,17 @@ 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.
> + */
> + if (default_mtime > 0xffffffff) {
> + fprintf(stderr, "ERROR: Timestamp 0x%08x too large for cpio format\n",
"0x%08x" is at least missing an 'l'. Possibly, showing the invalid
timestamp does not make much sense. If someone feeds the string
"1607420928" into KBUILD_BUILD_TIMESTAMP, as written in the commit
message, $(date -d $KBUILD_BUILD_TIMESTAMP +%s) returns a value that
will probably not be helpful.
Sorry for the noise; v3 follows.
> + default_mtime);
> + exit(1);
> + }
> +
> if (argc - optind != 1) {
> usage(argv[0]);
> exit(1);
> --
> 2.30.1
--
epost|xmpp: nicolas@xxxxxxxxx irc://oftc.net/nsc
↳ gpg: 18ed 52db e34f 860e e9fb c82b 7d97 0932 55a0 ce7f
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