Commit 4c9d410f authored Oct 12, 2021 by Nicolas Schier Committed by Masahiro Yamada Oct 24, 2021

initramfs: Check timestamp to prevent broken cpio archive

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 9:48:48 UTC) 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@fjasle.eu>
Cc: Thomas Kühnel <thomas.kuehnel@avm.de>
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>

parent 6947fd96

usr/gen_init_cpio.c

+16 −0

Original line number	Diff line number	Diff line
		@@ -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 +557,16 @@ 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 too large for cpio format\n");
		exit(1);
		}

		if (argc - optind != 1) {
		usage(argv[0]);
		exit(1);