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authorEric W. Biederman <ebiederm@xmission.com>2017-07-16 22:36:59 -0500
committerEric W. Biederman <ebiederm@xmission.com>2017-07-24 14:30:28 -0500
commitcc731525f26af85a1c3537da41e0abd1d35e0bdb (patch)
tree5badfc64a4a161cc6bc869ca376b019aaa937d2f /kernel
parentd08477aa975e97f1dc64c0ae59cebf98520456ce (diff)
signal: Remove kernel interal si_code magic
struct siginfo is a union and the kernel since 2.4 has been hiding a union tag in the high 16bits of si_code using the values: __SI_KILL __SI_TIMER __SI_POLL __SI_FAULT __SI_CHLD __SI_RT __SI_MESGQ __SI_SYS While this looks plausible on the surface, in practice this situation has not worked well. - Injected positive signals are not copied to user space properly unless they have these magic high bits set. - Injected positive signals are not reported properly by signalfd unless they have these magic high bits set. - These kernel internal values leaked to userspace via ptrace_peek_siginfo - It was possible to inject these kernel internal values and cause the the kernel to misbehave. - Kernel developers got confused and expected these kernel internal values in userspace in kernel self tests. - Kernel developers got confused and set si_code to __SI_FAULT which is SI_USER in userspace which causes userspace to think an ordinary user sent the signal and that it was not kernel generated. - The values make it impossible to reorganize the code to transform siginfo_copy_to_user into a plain copy_to_user. As si_code must be massaged before being passed to userspace. So remove these kernel internal si codes and make the kernel code simpler and more maintainable. To replace these kernel internal magic si_codes introduce the helper function siginfo_layout, that takes a signal number and an si_code and computes which union member of siginfo is being used. Have siginfo_layout return an enumeration so that gcc will have enough information to warn if a switch statement does not handle all of union members. A couple of architectures have a messed up ABI that defines signal specific duplications of SI_USER which causes more special cases in siginfo_layout than I would like. The good news is only problem architectures pay the cost. Update all of the code that used the previous magic __SI_ values to use the new SIL_ values and to call siginfo_layout to get those values. Escept where not all of the cases are handled remove the defaults in the switch statements so that if a new case is missed in the future the lack will show up at compile time. Modify the code that copies siginfo si_code to userspace to just copy the value and not cast si_code to a short first. The high bits are no longer used to hold a magic union member. Fixup the siginfo header files to stop including the __SI_ values in their constants and for the headers that were missing it to properly update the number of si_codes for each signal type. The fixes to copy_siginfo_from_user32 implementations has the interesting property that several of them perviously should never have worked as the __SI_ values they depended up where kernel internal. With that dependency gone those implementations should work much better. The idea of not passing the __SI_ values out to userspace and then not reinserting them has been tested with criu and criu worked without changes. Ref: 2.4.0-test1 Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
Diffstat (limited to 'kernel')
-rw-r--r--kernel/exit.c4
-rw-r--r--kernel/ptrace.c6
-rw-r--r--kernel/signal.c72
3 files changed, 59 insertions, 23 deletions
diff --git a/kernel/exit.c b/kernel/exit.c
index c5548faa9f37..c8f23613df5b 100644
--- a/kernel/exit.c
+++ b/kernel/exit.c
@@ -1616,7 +1616,7 @@ SYSCALL_DEFINE5(waitid, int, which, pid_t, upid, struct siginfo __user *,
user_access_begin();
unsafe_put_user(signo, &infop->si_signo, Efault);
unsafe_put_user(0, &infop->si_errno, Efault);
- unsafe_put_user((short)info.cause, &infop->si_code, Efault);
+ unsafe_put_user(info.cause, &infop->si_code, Efault);
unsafe_put_user(info.pid, &infop->si_pid, Efault);
unsafe_put_user(info.uid, &infop->si_uid, Efault);
unsafe_put_user(info.status, &infop->si_status, Efault);
@@ -1742,7 +1742,7 @@ COMPAT_SYSCALL_DEFINE5(waitid,
user_access_begin();
unsafe_put_user(signo, &infop->si_signo, Efault);
unsafe_put_user(0, &infop->si_errno, Efault);
- unsafe_put_user((short)info.cause, &infop->si_code, Efault);
+ unsafe_put_user(info.cause, &infop->si_code, Efault);
unsafe_put_user(info.pid, &infop->si_pid, Efault);
unsafe_put_user(info.uid, &infop->si_uid, Efault);
unsafe_put_user(info.status, &infop->si_status, Efault);
diff --git a/kernel/ptrace.c b/kernel/ptrace.c
index 60f356d91060..84b1367935e4 100644
--- a/kernel/ptrace.c
+++ b/kernel/ptrace.c
@@ -728,8 +728,7 @@ static int ptrace_peek_siginfo(struct task_struct *child,
if (unlikely(in_compat_syscall())) {
compat_siginfo_t __user *uinfo = compat_ptr(data);
- if (copy_siginfo_to_user32(uinfo, &info) ||
- __put_user(info.si_code, &uinfo->si_code)) {
+ if (copy_siginfo_to_user32(uinfo, &info)) {
ret = -EFAULT;
break;
}
@@ -739,8 +738,7 @@ static int ptrace_peek_siginfo(struct task_struct *child,
{
siginfo_t __user *uinfo = (siginfo_t __user *) data;
- if (copy_siginfo_to_user(uinfo, &info) ||
- __put_user(info.si_code, &uinfo->si_code)) {
+ if (copy_siginfo_to_user(uinfo, &info)) {
ret = -EFAULT;
break;
}
diff --git a/kernel/signal.c b/kernel/signal.c
index caed9133ae52..6bd53c8189f0 100644
--- a/kernel/signal.c
+++ b/kernel/signal.c
@@ -2682,6 +2682,51 @@ COMPAT_SYSCALL_DEFINE2(rt_sigpending, compat_sigset_t __user *, uset,
}
#endif
+enum siginfo_layout siginfo_layout(int sig, int si_code)
+{
+ enum siginfo_layout layout = SIL_KILL;
+ if ((si_code > SI_USER) && (si_code < SI_KERNEL)) {
+ static const struct {
+ unsigned char limit, layout;
+ } filter[] = {
+ [SIGILL] = { NSIGILL, SIL_FAULT },
+ [SIGFPE] = { NSIGFPE, SIL_FAULT },
+ [SIGSEGV] = { NSIGSEGV, SIL_FAULT },
+ [SIGBUS] = { NSIGBUS, SIL_FAULT },
+ [SIGTRAP] = { NSIGTRAP, SIL_FAULT },
+#if defined(SIGMET) && defined(NSIGEMT)
+ [SIGEMT] = { NSIGEMT, SIL_FAULT },
+#endif
+ [SIGCHLD] = { NSIGCHLD, SIL_CHLD },
+ [SIGPOLL] = { NSIGPOLL, SIL_POLL },
+#ifdef __ARCH_SIGSYS
+ [SIGSYS] = { NSIGSYS, SIL_SYS },
+#endif
+ };
+ if ((sig < ARRAY_SIZE(filter)) && (si_code <= filter[sig].limit))
+ layout = filter[sig].layout;
+ else if (si_code <= NSIGPOLL)
+ layout = SIL_POLL;
+ } else {
+ if (si_code == SI_TIMER)
+ layout = SIL_TIMER;
+ else if (si_code == SI_SIGIO)
+ layout = SIL_POLL;
+ else if (si_code < 0)
+ layout = SIL_RT;
+ /* Tests to support buggy kernel ABIs */
+#ifdef TRAP_FIXME
+ if ((sig == SIGTRAP) && (si_code == TRAP_FIXME))
+ layout = SIL_FAULT;
+#endif
+#ifdef FPE_FIXME
+ if ((sig == SIGFPE) && (si_code == FPE_FIXME))
+ layout = SIL_FAULT;
+#endif
+ }
+ return layout;
+}
+
#ifndef HAVE_ARCH_COPY_SIGINFO_TO_USER
int copy_siginfo_to_user(siginfo_t __user *to, const siginfo_t *from)
@@ -2704,22 +2749,20 @@ int copy_siginfo_to_user(siginfo_t __user *to, const siginfo_t *from)
*/
err = __put_user(from->si_signo, &to->si_signo);
err |= __put_user(from->si_errno, &to->si_errno);
- err |= __put_user((short)from->si_code, &to->si_code);
- switch (from->si_code & __SI_MASK) {
- case __SI_KILL:
+ err |= __put_user(from->si_code, &to->si_code);
+ switch (siginfo_layout(from->si_signo, from->si_code)) {
+ case SIL_KILL:
err |= __put_user(from->si_pid, &to->si_pid);
err |= __put_user(from->si_uid, &to->si_uid);
break;
- case __SI_TIMER:
- err |= __put_user(from->si_tid, &to->si_tid);
- err |= __put_user(from->si_overrun, &to->si_overrun);
- err |= __put_user(from->si_ptr, &to->si_ptr);
+ case SIL_TIMER:
+ /* Unreached SI_TIMER is negative */
break;
- case __SI_POLL:
+ case SIL_POLL:
err |= __put_user(from->si_band, &to->si_band);
err |= __put_user(from->si_fd, &to->si_fd);
break;
- case __SI_FAULT:
+ case SIL_FAULT:
err |= __put_user(from->si_addr, &to->si_addr);
#ifdef __ARCH_SI_TRAPNO
err |= __put_user(from->si_trapno, &to->si_trapno);
@@ -2744,30 +2787,25 @@ int copy_siginfo_to_user(siginfo_t __user *to, const siginfo_t *from)
err |= __put_user(from->si_pkey, &to->si_pkey);
#endif
break;
- case __SI_CHLD:
+ case SIL_CHLD:
err |= __put_user(from->si_pid, &to->si_pid);
err |= __put_user(from->si_uid, &to->si_uid);
err |= __put_user(from->si_status, &to->si_status);
err |= __put_user(from->si_utime, &to->si_utime);
err |= __put_user(from->si_stime, &to->si_stime);
break;
- case __SI_RT: /* This is not generated by the kernel as of now. */
- case __SI_MESGQ: /* But this is */
+ case SIL_RT:
err |= __put_user(from->si_pid, &to->si_pid);
err |= __put_user(from->si_uid, &to->si_uid);
err |= __put_user(from->si_ptr, &to->si_ptr);
break;
#ifdef __ARCH_SIGSYS
- case __SI_SYS:
+ case SIL_SYS:
err |= __put_user(from->si_call_addr, &to->si_call_addr);
err |= __put_user(from->si_syscall, &to->si_syscall);
err |= __put_user(from->si_arch, &to->si_arch);
break;
#endif
- default: /* this is just in case for now ... */
- err |= __put_user(from->si_pid, &to->si_pid);
- err |= __put_user(from->si_uid, &to->si_uid);
- break;
}
return err;
}