From 4c9d410f32b3fac15ff1197c4b8746da6d11a17e Mon Sep 17 00:00:00 2001 From: Nicolas Schier Date: Tue, 12 Oct 2021 20:12:20 +0000 Subject: initramfs: Check timestamp to prevent broken cpio archive MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit 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 Cc: Thomas Kühnel Signed-off-by: Masahiro Yamada --- usr/gen_init_cpio.c | 16 ++++++++++++++++ 1 file changed, 16 insertions(+) (limited to 'usr') diff --git a/usr/gen_init_cpio.c b/usr/gen_init_cpio.c index bf5b98c6cf8d..0e2c8a5838b1 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); -- cgit