3.16.58-rc1 review patch. If anyone has any objections, please let me know.
------------------
From: Kees Cook keescook@chromium.org
commit 48dc92b9fc3926844257316e75ba11eb5c742b2c upstream.
This adds the new "seccomp" syscall with both an "operation" and "flags" parameter for future expansion. The third argument is a pointer value, used with the SECCOMP_SET_MODE_FILTER operation. Currently, flags must be 0. This is functionally equivalent to prctl(PR_SET_SECCOMP, ...).
In addition to the TSYNC flag later in this patch series, there is a non-zero chance that this syscall could be used for configuring a fixed argument area for seccomp-tracer-aware processes to pass syscall arguments in the future. Hence, the use of "seccomp" not simply "seccomp_add_filter" for this syscall. Additionally, this syscall uses operation, flags, and user pointer for arguments because strictly passing arguments via a user pointer would mean seccomp itself would be unable to trivially filter the seccomp syscall itself.
Signed-off-by: Kees Cook keescook@chromium.org Reviewed-by: Oleg Nesterov oleg@redhat.com Reviewed-by: Andy Lutomirski luto@amacapital.net Signed-off-by: Ben Hutchings ben@decadent.org.uk --- arch/Kconfig | 1 + arch/x86/syscalls/syscall_32.tbl | 1 + arch/x86/syscalls/syscall_64.tbl | 1 + include/linux/syscalls.h | 2 ++ include/uapi/asm-generic/unistd.h | 4 ++- include/uapi/linux/seccomp.h | 4 +++ kernel/seccomp.c | 55 ++++++++++++++++++++++++++++--- kernel/sys_ni.c | 3 ++ 8 files changed, 65 insertions(+), 6 deletions(-)
--- a/arch/Kconfig +++ b/arch/Kconfig @@ -321,6 +321,7 @@ config HAVE_ARCH_SECCOMP_FILTER - secure_computing is called from a ptrace_event()-safe context - secure_computing return value is checked and a return value of -1 results in the system call being skipped immediately. + - seccomp syscall wired up
config SECCOMP_FILTER def_bool y --- a/arch/x86/syscalls/syscall_32.tbl +++ b/arch/x86/syscalls/syscall_32.tbl @@ -360,3 +360,4 @@ 351 i386 sched_setattr sys_sched_setattr 352 i386 sched_getattr sys_sched_getattr 353 i386 renameat2 sys_renameat2 +354 i386 seccomp sys_seccomp --- a/arch/x86/syscalls/syscall_64.tbl +++ b/arch/x86/syscalls/syscall_64.tbl @@ -323,6 +323,7 @@ 314 common sched_setattr sys_sched_setattr 315 common sched_getattr sys_sched_getattr 316 common renameat2 sys_renameat2 +317 common seccomp sys_seccomp
# # x32-specific system call numbers start at 512 to avoid cache impact --- a/include/linux/syscalls.h +++ b/include/linux/syscalls.h @@ -866,4 +866,6 @@ asmlinkage long sys_process_vm_writev(pi asmlinkage long sys_kcmp(pid_t pid1, pid_t pid2, int type, unsigned long idx1, unsigned long idx2); asmlinkage long sys_finit_module(int fd, const char __user *uargs, int flags); +asmlinkage long sys_seccomp(unsigned int op, unsigned int flags, + const char __user *uargs); #endif --- a/include/uapi/asm-generic/unistd.h +++ b/include/uapi/asm-generic/unistd.h @@ -699,9 +699,11 @@ __SYSCALL(__NR_sched_setattr, sys_sched_ __SYSCALL(__NR_sched_getattr, sys_sched_getattr) #define __NR_renameat2 276 __SYSCALL(__NR_renameat2, sys_renameat2) +#define __NR_seccomp 277 +__SYSCALL(__NR_seccomp, sys_seccomp)
#undef __NR_syscalls -#define __NR_syscalls 277 +#define __NR_syscalls 278
/* * All syscalls below here should go away really, --- a/include/uapi/linux/seccomp.h +++ b/include/uapi/linux/seccomp.h @@ -10,6 +10,10 @@ #define SECCOMP_MODE_STRICT 1 /* uses hard-coded filter. */ #define SECCOMP_MODE_FILTER 2 /* uses user-supplied filter. */
+/* Valid operations for seccomp syscall. */ +#define SECCOMP_SET_MODE_STRICT 0 +#define SECCOMP_SET_MODE_FILTER 1 + /* * All BPF programs must return a 32-bit value. * The bottom 16-bits are for optional return data. --- a/kernel/seccomp.c +++ b/kernel/seccomp.c @@ -18,6 +18,7 @@ #include <linux/compat.h> #include <linux/sched.h> #include <linux/seccomp.h> +#include <linux/syscalls.h>
/* #define SECCOMP_DEBUG 1 */
@@ -314,7 +315,7 @@ free_prog: * * Returns 0 on success and non-zero otherwise. */ -static long seccomp_attach_user_filter(char __user *user_filter) +static long seccomp_attach_user_filter(const char __user *user_filter) { struct sock_fprog fprog; long ret = -EFAULT; @@ -517,6 +518,7 @@ out: #ifdef CONFIG_SECCOMP_FILTER /** * seccomp_set_mode_filter: internal function for setting seccomp filter + * @flags: flags to change filter behavior * @filter: struct sock_fprog containing filter * * This function may be called repeatedly to install additional filters. @@ -527,11 +529,16 @@ out: * * Returns 0 on success or -EINVAL on failure. */ -static long seccomp_set_mode_filter(char __user *filter) +static long seccomp_set_mode_filter(unsigned int flags, + const char __user *filter) { const unsigned long seccomp_mode = SECCOMP_MODE_FILTER; long ret = -EINVAL;
+ /* Validate flags. */ + if (flags != 0) + goto out; + if (!seccomp_may_assign_mode(seccomp_mode)) goto out;
@@ -544,12 +551,35 @@ out: return ret; } #else -static inline long seccomp_set_mode_filter(char __user *filter) +static inline long seccomp_set_mode_filter(unsigned int flags, + const char __user *filter) { return -EINVAL; } #endif
+/* Common entry point for both prctl and syscall. */ +static long do_seccomp(unsigned int op, unsigned int flags, + const char __user *uargs) +{ + switch (op) { + case SECCOMP_SET_MODE_STRICT: + if (flags != 0 || uargs != NULL) + return -EINVAL; + return seccomp_set_mode_strict(); + case SECCOMP_SET_MODE_FILTER: + return seccomp_set_mode_filter(flags, uargs); + default: + return -EINVAL; + } +} + +SYSCALL_DEFINE3(seccomp, unsigned int, op, unsigned int, flags, + const char __user *, uargs) +{ + return do_seccomp(op, flags, uargs); +} + /** * prctl_set_seccomp: configures current->seccomp.mode * @seccomp_mode: requested mode to use @@ -559,12 +589,27 @@ static inline long seccomp_set_mode_filt */ long prctl_set_seccomp(unsigned long seccomp_mode, char __user *filter) { + unsigned int op; + char __user *uargs; + switch (seccomp_mode) { case SECCOMP_MODE_STRICT: - return seccomp_set_mode_strict(); + op = SECCOMP_SET_MODE_STRICT; + /* + * Setting strict mode through prctl always ignored filter, + * so make sure it is always NULL here to pass the internal + * check in do_seccomp(). + */ + uargs = NULL; + break; case SECCOMP_MODE_FILTER: - return seccomp_set_mode_filter(filter); + op = SECCOMP_SET_MODE_FILTER; + uargs = filter; + break; default: return -EINVAL; } + + /* prctl interface doesn't have flags, so they are always zero. */ + return do_seccomp(op, 0, uargs); } --- a/kernel/sys_ni.c +++ b/kernel/sys_ni.c @@ -213,3 +213,6 @@ cond_syscall(compat_sys_open_by_handle_a
/* compare kernel pointers */ cond_syscall(sys_kcmp); + +/* operate on Secure Computing state */ +cond_syscall(sys_seccomp);