* [PATCH] initramfs: Check timestamp to prevent broken cpio archive
@ 2021-10-07 18:59 Nicolas Schier
2021-10-12 2:02 ` Masahiro Yamada
0 siblings, 1 reply; 4+ messages in thread
From: Nicolas Schier @ 2021-10-07 18:59 UTC (permalink / raw)
To: linux-kernel, linux-kbuild; +Cc: Nicolas Schier, Thomas Kühnel
Cpio format reserves 8 bytes for an ASCII representation of a time_t timestamp.
While 2106-02-07 06:28:15 (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
results 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@fjasle.eu>
Cc: Thomas Kühnel <thomas.kuehnel@avm.de>
---
usr/gen_init_cpio.c | 17 +++++++++++++++++
1 file changed, 17 insertions(+)
diff --git a/usr/gen_init_cpio.c b/usr/gen_init_cpio.c
index 03b21189d58b..983dcdd35925 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 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
^ permalink raw reply related [flat|nested] 4+ messages in thread
* Re: [PATCH] initramfs: Check timestamp to prevent broken cpio archive
2021-10-07 18:59 [PATCH] initramfs: Check timestamp to prevent broken cpio archive Nicolas Schier
@ 2021-10-12 2:02 ` Masahiro Yamada
2021-10-12 8:29 ` Nicolas Schier
0 siblings, 1 reply; 4+ messages in thread
From: Masahiro Yamada @ 2021-10-12 2:02 UTC (permalink / raw)
To: Nicolas Schier
Cc: Linux Kernel Mailing List, Linux Kbuild mailing list, Thomas Kühnel
On Fri, Oct 8, 2021 at 3:59 AM Nicolas Schier <nicolas@fjasle.eu> wrote:
>
> Cpio format reserves 8 bytes for an ASCII representation of a time_t timestamp.
> While 2106-02-07 06:28:15 (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
> results in a broken cpio archive. Add timestamp checks to prevent overrun of
> the 8-byte cpio header field.
Out of curiosity, how did you figure out
"2106-02-07 06:28:15" was the overflow point?
Is it affected by leap seconds?
I got ffff816f
$ printf "%x" $(date -d'2106-02-07 06:28:15' +%s)
ffff816f
> 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@fjasle.eu>
> Cc: Thomas Kühnel <thomas.kuehnel@avm.de>
> ---
> usr/gen_init_cpio.c | 17 +++++++++++++++++
> 1 file changed, 17 insertions(+)
>
> diff --git a/usr/gen_init_cpio.c b/usr/gen_init_cpio.c
> index 03b21189d58b..983dcdd35925 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 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
>
--
Best Regards
Masahiro Yamada
^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: [PATCH] initramfs: Check timestamp to prevent broken cpio archive
2021-10-12 2:02 ` Masahiro Yamada
@ 2021-10-12 8:29 ` Nicolas Schier
2021-10-13 1:40 ` Masahiro Yamada
0 siblings, 1 reply; 4+ messages in thread
From: Nicolas Schier @ 2021-10-12 8:29 UTC (permalink / raw)
To: Masahiro Yamada
Cc: Linux Kernel Mailing List, Linux Kbuild mailing list, Thomas Kühnel
On Tue, Oct 12, 2021 at 11:02:33AM +0900, Masahiro Yamada wrote:
> Date: Tue, 12 Oct 2021 11:02:33 +0900
> From: Masahiro Yamada <masahiroy@kernel.org>
> To: Nicolas Schier <nicolas@fjasle.eu>
> Cc: Linux Kernel Mailing List <linux-kernel@vger.kernel.org>, Linux Kbuild
> mailing list <linux-kbuild@vger.kernel.org>, Thomas Kühnel
> <thomas.kuehnel@avm.de>
> Subject: Re: [PATCH] initramfs: Check timestamp to prevent broken cpio
> archive
> Message-ID: <CAK7LNASDu7RK0vLtx1991abx880DtQHK+U2FK3qKbH5Kcz3ipw@mail.gmail.com>
>
> On Fri, Oct 8, 2021 at 3:59 AM Nicolas Schier <nicolas@fjasle.eu> wrote:
> >
> > Cpio format reserves 8 bytes for an ASCII representation of a time_t timestamp.
> > While 2106-02-07 06:28:15 (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
> > results in a broken cpio archive. Add timestamp checks to prevent overrun of
> > the 8-byte cpio header field.
>
> Out of curiosity, how did you figure out
> "2106-02-07 06:28:15" was the overflow point?
> Is it affected by leap seconds?
>
>
> I got ffff816f
>
>
> $ printf "%x" $(date -d'2106-02-07 06:28:15' +%s)
> ffff816f
You have a local time zone offset of -9h?
I just did
$ TZ=UTC date -d@$((0xffffffff))
Sun Feb 7 06:28:15 UTC 2106
I should have mentioned the time zone info in the commit message.
> > 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@fjasle.eu>
> > Cc: Thomas Kühnel <thomas.kuehnel@avm.de>
> > ---
> > usr/gen_init_cpio.c | 17 +++++++++++++++++
> > 1 file changed, 17 insertions(+)
> >
> > diff --git a/usr/gen_init_cpio.c b/usr/gen_init_cpio.c
> > index 03b21189d58b..983dcdd35925 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 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
> >
>
>
> --
> Best Regards
> Masahiro Yamada
--
epost|xmpp: nicolas@fjasle.eu irc://oftc.net/nsc
↳ gpg: 18ed 52db e34f 860e e9fb c82b 7d97 0932 55a0 ce7f
-- frykten for herren er opphav til kunnskap --
^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: [PATCH] initramfs: Check timestamp to prevent broken cpio archive
2021-10-12 8:29 ` Nicolas Schier
@ 2021-10-13 1:40 ` Masahiro Yamada
0 siblings, 0 replies; 4+ messages in thread
From: Masahiro Yamada @ 2021-10-13 1:40 UTC (permalink / raw)
To: Masahiro Yamada, Linux Kernel Mailing List,
Linux Kbuild mailing list, Thomas Kühnel
On Tue, Oct 12, 2021 at 5:29 PM Nicolas Schier <nicolas@fjasle.eu> wrote:
>
> On Tue, Oct 12, 2021 at 11:02:33AM +0900, Masahiro Yamada wrote:
> > Date: Tue, 12 Oct 2021 11:02:33 +0900
> > From: Masahiro Yamada <masahiroy@kernel.org>
> > To: Nicolas Schier <nicolas@fjasle.eu>
> > Cc: Linux Kernel Mailing List <linux-kernel@vger.kernel.org>, Linux Kbuild
> > mailing list <linux-kbuild@vger.kernel.org>, Thomas Kühnel
> > <thomas.kuehnel@avm.de>
> > Subject: Re: [PATCH] initramfs: Check timestamp to prevent broken cpio
> > archive
> > Message-ID: <CAK7LNASDu7RK0vLtx1991abx880DtQHK+U2FK3qKbH5Kcz3ipw@mail.gmail.com>
> >
> > On Fri, Oct 8, 2021 at 3:59 AM Nicolas Schier <nicolas@fjasle.eu> wrote:
> > >
> > > Cpio format reserves 8 bytes for an ASCII representation of a time_t timestamp.
> > > While 2106-02-07 06:28:15 (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
> > > results in a broken cpio archive. Add timestamp checks to prevent overrun of
> > > the 8-byte cpio header field.
> >
> > Out of curiosity, how did you figure out
> > "2106-02-07 06:28:15" was the overflow point?
> > Is it affected by leap seconds?
> >
> >
> > I got ffff816f
> >
> >
> > $ printf "%x" $(date -d'2106-02-07 06:28:15' +%s)
> > ffff816f
>
> You have a local time zone offset of -9h?
> I just did
>
> $ TZ=UTC date -d@$((0xffffffff))
> Sun Feb 7 06:28:15 UTC 2106
>
> I should have mentioned the time zone info in the commit message.
>
Ah, time zone!
Right, my time zone is JST (+09:00).
And, thanks for the update.
>
>
> > > 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@fjasle.eu>
> > > Cc: Thomas Kühnel <thomas.kuehnel@avm.de>
> > > ---
> > > usr/gen_init_cpio.c | 17 +++++++++++++++++
> > > 1 file changed, 17 insertions(+)
> > >
> > > diff --git a/usr/gen_init_cpio.c b/usr/gen_init_cpio.c
> > > index 03b21189d58b..983dcdd35925 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 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
> > >
> >
> >
> > --
> > Best Regards
> > Masahiro Yamada
>
> --
> epost|xmpp: nicolas@fjasle.eu irc://oftc.net/nsc
> ↳ gpg: 18ed 52db e34f 860e e9fb c82b 7d97 0932 55a0 ce7f
> -- frykten for herren er opphav til kunnskap --
--
Best Regards
Masahiro Yamada
^ permalink raw reply [flat|nested] 4+ messages in thread
end of thread, other threads:[~2021-10-13 1:41 UTC | newest]
Thread overview: 4+ messages (download: mbox.gz / follow: Atom feed)
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2021-10-07 18:59 [PATCH] initramfs: Check timestamp to prevent broken cpio archive Nicolas Schier
2021-10-12 2:02 ` Masahiro Yamada
2021-10-12 8:29 ` Nicolas Schier
2021-10-13 1:40 ` Masahiro Yamada
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