signal: fix information leak in copy_siginfo_from_user32

This function can leak kernel stack data when the user siginfo_t has a
positive si_code value.  The top 16 bits of si_code descibe which fields
in the siginfo_t union are active, but they are treated inconsistently
between copy_siginfo_from_user32, copy_siginfo_to_user32 and
copy_siginfo_to_user.

copy_siginfo_from_user32 is called from rt_sigqueueinfo and
rt_tgsigqueueinfo in which the user has full control overthe top 16 bits
of si_code.

This fixes the following information leaks:
x86:   8 bytes leaked when sending a signal from a 32-bit process to
       itself. This leak grows to 16 bytes if the process uses x32.
       (si_code = __SI_CHLD)
x86:   100 bytes leaked when sending a signal from a 32-bit process to
       a 64-bit process. (si_code = -1)
sparc: 4 bytes leaked when sending a signal from a 32-bit process to a
       64-bit process. (si_code = any)

parsic and s390 have similar bugs, but they are not vulnerable because
rt_[tg]sigqueueinfo have checks that prevent sending a positive si_code
to a different process.  These bugs are also fixed for consistency.

Signed-off-by: Amanieu d'Antras <amanieu@gmail.com>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Russell King <rmk@arm.linux.org.uk>
Cc: Ralf Baechle <ralf@linux-mips.org>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Chris Metcalf <cmetcalf@ezchip.com>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 2 insertions, 2 deletions

diff --git a/kernel/signal.c b/kernel/signal.c
index 836df8dac6cc..00524cf6c412 100644
--- a/kernel/signal.c
+++ b/kernel/signal.c
@@ -3017,7 +3017,7 @@ COMPAT_SYSCALL_DEFINE3(rt_sigqueueinfo,
                         int, sig,
                         struct compat_siginfo __user *, uinfo)
 {
-        siginfo_t info;
+        siginfo_t info = {};
         int ret = copy_siginfo_from_user32(&info, uinfo);
         if (unlikely(ret))
                 return ret;
@@ -3061,7 +3061,7 @@ COMPAT_SYSCALL_DEFINE4(rt_tgsigqueueinfo,
                         int, sig,
                         struct compat_siginfo __user *, uinfo)
 {
-        siginfo_t info;
+        siginfo_t info = {};
 
         if (copy_siginfo_from_user32(&info, uinfo))
                 return -EFAULT;