From 6613c6f28432bd0e835f4a7516e1e766927de123 Mon Sep 17 00:00:00 2001
From: Nicolas Schier <nicolas@fjasle.eu>
Date: Tue, 12 Oct 2021 20:12:20 +0000
Subject: [PATCH] initramfs: Check timestamp to prevent broken cpio archive
MIME-Version: 1.0
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Git-commit: 4c9d410f32b3fac15ff1197c4b8746da6d11a17e
Patch-mainline: v5.16-rc1
References: bsc#1193289
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>
Reviewed-by: David Disseldorp <ddiss@suse.de>
---
usr/gen_init_cpio.c | 16 ++++++++++++++++
1 file changed, 16 insertions(+)
diff --git a/usr/gen_init_cpio.c b/usr/gen_init_cpio.c
index 03b21189d58b..97aeeecf7386 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 +557,16 @@ 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);
--
2.35.3