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",
+ default_mtime);
+ exit(1);
+ }
+
if (argc - optind != 1) {
usage(argv[0]);
exit(1);
--
2.30.1
