[PATCH] compat: Fix RT signal mask corruption via sigprocmask

From: Jan Kiszka
Date: Wed May 09 2012 - 18:10:32 EST

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 the signal mask and caused RT signal
unblocking this way.

Signed-off-by: Jan Kiszka <jan.kiszka@xxxxxxxxxxx>
kernel/compat.c | 2 ++
1 files changed, 2 insertions(+), 0 deletions(-)

diff --git a/kernel/compat.c b/kernel/compat.c
index 74ff849..03e491d 100644
--- a/kernel/compat.c
+++ b/kernel/compat.c
@@ -381,6 +381,8 @@ asmlinkage long compat_sys_sigprocmask(int how, compat_old_sigset_t __user *set,

if (set && get_user(s, set))
return -EFAULT;
+ s |= current->blocked.sig[0] &
+ ~((old_sigset_t)(compat_old_sigset_t)-1);
old_fs = get_fs();
ret = sys_sigprocmask(how,
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