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Subject[ 43/54] compat: Fix RT signal mask corruption via sigprocmask
3.0-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Jan Kiszka <jan.kiszka@siemens.com>

commit b7dafa0ef3145c31d7753be0a08b3cbda51f0209 upstream.

compat_sys_sigprocmask reads a smaller signal mask from userspace than
sigprogmask accepts for setting. So the high word of blocked.sig[0]
will be cleared, releasing any potentially blocked RT signal.

This was discovered via userspace code that relies on get/setcontext.
glibc's i386 versions of those functions use sigprogmask instead of
rt_sigprogmask to save/restore signal mask and caused RT signal
unblocking this way.

As suggested by Linus, this replaces the sys_sigprocmask based compat
version with one that open-codes the required logic, including the merge
of the existing blocked set with the new one provided on SIG_SETMASK.

Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
kernel/compat.c | 65 ++++++++++++++++++++++++++++++++++++++++----------------
1 file changed, 47 insertions(+), 18 deletions(-)

--- a/kernel/compat.c
+++ b/kernel/compat.c
@@ -318,25 +318,54 @@ asmlinkage long compat_sys_sigpending(co

#ifdef __ARCH_WANT_SYS_SIGPROCMASK

-asmlinkage long compat_sys_sigprocmask(int how, compat_old_sigset_t __user *set,
- compat_old_sigset_t __user *oset)
+/*
+ * sys_sigprocmask SIG_SETMASK sets the first (compat) word of the
+ * blocked set of signals to the supplied signal set
+ */
+static inline void compat_sig_setmask(sigset_t *blocked, compat_sigset_word set)
{
- old_sigset_t s;
- long ret;
- mm_segment_t old_fs;
-
- if (set && get_user(s, set))
- return -EFAULT;
- old_fs = get_fs();
- set_fs(KERNEL_DS);
- ret = sys_sigprocmask(how,
- set ? (old_sigset_t __user *) &s : NULL,
- oset ? (old_sigset_t __user *) &s : NULL);
- set_fs(old_fs);
- if (ret == 0)
- if (oset)
- ret = put_user(s, oset);
- return ret;
+ memcpy(blocked->sig, &set, sizeof(set));
+}
+
+asmlinkage long compat_sys_sigprocmask(int how,
+ compat_old_sigset_t __user *nset,
+ compat_old_sigset_t __user *oset)
+{
+ old_sigset_t old_set, new_set;
+ sigset_t new_blocked;
+
+ old_set = current->blocked.sig[0];
+
+ if (nset) {
+ if (get_user(new_set, nset))
+ return -EFAULT;
+ new_set &= ~(sigmask(SIGKILL) | sigmask(SIGSTOP));
+
+ new_blocked = current->blocked;
+
+ switch (how) {
+ case SIG_BLOCK:
+ sigaddsetmask(&new_blocked, new_set);
+ break;
+ case SIG_UNBLOCK:
+ sigdelsetmask(&new_blocked, new_set);
+ break;
+ case SIG_SETMASK:
+ compat_sig_setmask(&new_blocked, new_set);
+ break;
+ default:
+ return -EINVAL;
+ }
+
+ set_current_blocked(&new_blocked);
+ }
+
+ if (oset) {
+ if (put_user(old_set, oset))
+ return -EFAULT;
+ }
+
+ return 0;
}

#endif



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