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compat: Fix RT signal mask corruption via sigprocmask 

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>
This commit is contained in:
Jan Kiszka 2012-05-10 10:04:36 -03:00 committed by Linus Torvalds
parent 7ee94d97aa
commit b7dafa0ef3
1 changed files with 46 additions and 17 deletions
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63
kernel/compat.c
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@ -372,25 +372,54 @@ asmlinkage long compat_sys_sigpending(compat_old_sigset_t __user *set)
#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;
memcpy(blocked->sig, &set, sizeof(set));
}
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;
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