[PATCH] samples/seccomp: fix endianness bug in LO_ARG define

[PATCH] samples/seccomp: fix endianness bug in LO_ARG define

[Heiko Carstens]

From: Heiko Carstens <heiko.carstens@de.ibm.com>

The LO_ARG define needs to consider endianness also for 32 bit builds.

The "bpf_fancy" test case didn't work on s390 in 32 bit and compat mode
because the LO_ARG define resulted in a BPF program which read the upper
halve of the 64 bit system call arguments instead of the lower halves.

Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>
---
 samples/seccomp/bpf-helper.h | 15 ++++++++++-----
 1 file changed, 10 insertions(+), 5 deletions(-)

diff --git a/samples/seccomp/bpf-helper.h b/samples/seccomp/bpf-helper.h
index 643279d..38ee70f 100644
--- a/samples/seccomp/bpf-helper.h
+++ b/samples/seccomp/bpf-helper.h
@@ -59,6 +59,16 @@ void seccomp_bpf_print(struct sock_filter *filter, size_t count);
 #define FIND_LABEL(labels, label) seccomp_bpf_label((labels), #label)
 
 #define EXPAND(...) __VA_ARGS__
+
+/* Ensure that we load the logically correct offset. */
+#if __BYTE_ORDER == __LITTLE_ENDIAN
+#define LO_ARG(idx) offsetof(struct seccomp_data, args[(idx)])
+#elif __BYTE_ORDER == __BIG_ENDIAN
+#define LO_ARG(idx) offsetof(struct seccomp_data, args[(idx)]) + sizeof(__u32)
+#else
+#error "Unknown endianness"
+#endif
+
 /* Map all width-sensitive operations */
 #if __BITS_PER_LONG == 32
 
@@ -70,21 +80,16 @@ void seccomp_bpf_print(struct sock_filter *filter, size_t count);
 #define JLE(x, jt) JLE32(x, EXPAND(jt))
 #define JA(x, jt) JA32(x, EXPAND(jt))
 #define ARG(i) ARG_32(i)
-#define LO_ARG(idx) offsetof(struct seccomp_data, args[(idx)])
 
 #elif __BITS_PER_LONG == 64
 
 /* Ensure that we load the logically correct offset. */
 #if __BYTE_ORDER == __LITTLE_ENDIAN
 #define ENDIAN(_lo, _hi) _lo, _hi
-#define LO_ARG(idx) offsetof(struct seccomp_data, args[(idx)])
 #define HI_ARG(idx) offsetof(struct seccomp_data, args[(idx)]) + sizeof(__u32)
 #elif __BYTE_ORDER == __BIG_ENDIAN
 #define ENDIAN(_lo, _hi) _hi, _lo
-#define LO_ARG(idx) offsetof(struct seccomp_data, args[(idx)]) + sizeof(__u32)
 #define HI_ARG(idx) offsetof(struct seccomp_data, args[(idx)])
-#else
-#error "Unknown endianness"
 #endif
 
 union arg64 {
-- 
1.7.11.4

Re: [PATCH] samples/seccomp: fix endianness bug in LO_ARG define

[Kees Cook]

On Tue, Jul 31, 2012 at 7:15 AM, Heiko Carstens
<heiko.carstens@de.ibm.com> wrote:
> From: Heiko Carstens <heiko.carstens@de.ibm.com>
>
> The LO_ARG define needs to consider endianness also for 32 bit builds.
>
> The "bpf_fancy" test case didn't work on s390 in 32 bit and compat mode
> because the LO_ARG define resulted in a BPF program which read the upper
> halve of the 64 bit system call arguments instead of the lower halves.
>
> Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>

Good catch; thanks for the fix!

Acked-by: Kees Cook <keescook@chromium.org>

-Kees

-- 
Kees Cook
Chrome OS Security

Re: [PATCH] samples/seccomp: fix endianness bug in LO_ARG define

[James Morris]

On Tue, 31 Jul 2012, Kees Cook wrote:

> On Tue, Jul 31, 2012 at 7:15 AM, Heiko Carstens
> <heiko.carstens@de.ibm.com> wrote:
> > From: Heiko Carstens <heiko.carstens@de.ibm.com>
> >
> > The LO_ARG define needs to consider endianness also for 32 bit builds.
> >
> > The "bpf_fancy" test case didn't work on s390 in 32 bit and compat mode
> > because the LO_ARG define resulted in a BPF program which read the upper
> > halve of the 64 bit system call arguments instead of the lower halves.
> >
> > Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>
> 
> Good catch; thanks for the fix!
> 
> Acked-by: Kees Cook <keescook@chromium.org>

Applied to
git://git.kernel.org/pub/scm/linux/kernel/git/jmorris/linux-security.git next


-- 
James Morris
<jmorris@namei.org>