--- /dev/null
+From c41d68a513c71e35a14f66d71782d27a79a81ea6 Mon Sep 17 00:00:00 2001
+From: H. Peter Anvin <hpa@linux.intel.com>
+Date: Tue, 7 Sep 2010 16:16:18 -0700
+Subject: [PATCH] compat: Make compat_alloc_user_space() incorporate the access_ok()
+
+compat_alloc_user_space() expects the caller to independently call
+access_ok() to verify the returned area. A missing call could
+introduce problems on some architectures.
+
+This patch incorporates the access_ok() check into
+compat_alloc_user_space() and also adds a sanity check on the length.
+The existing compat_alloc_user_space() implementations are renamed
+arch_compat_alloc_user_space() and are used as part of the
+implementation of the new global function.
+
+This patch assumes NULL will cause __get_user()/__put_user() to either
+fail or access userspace on all architectures. This should be
+followed by checking the return value of compat_access_user_space()
+for NULL in the callers, at which time the access_ok() in the callers
+can also be removed.
+
+Reported-by: Ben Hawkes <hawkes@sota.gen.nz>
+Signed-off-by: H. Peter Anvin <hpa@linux.intel.com>
+Acked-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
+Acked-by: Chris Metcalf <cmetcalf@tilera.com>
+Acked-by: David S. Miller <davem@davemloft.net>
+Acked-by: Ingo Molnar <mingo@elte.hu>
+Acked-by: Thomas Gleixner <tglx@linutronix.de>
+Acked-by: Tony Luck <tony.luck@intel.com>
+Cc: Andrew Morton <akpm@linux-foundation.org>
+Cc: Arnd Bergmann <arnd@arndb.de>
+Cc: Fenghua Yu <fenghua.yu@intel.com>
+Cc: H. Peter Anvin <hpa@zytor.com>
+Cc: Heiko Carstens <heiko.carstens@de.ibm.com>
+Cc: Helge Deller <deller@gmx.de>
+Cc: James Bottomley <jejb@parisc-linux.org>
+Cc: Kyle McMartin <kyle@mcmartin.ca>
+Cc: Martin Schwidefsky <schwidefsky@de.ibm.com>
+Cc: Paul Mackerras <paulus@samba.org>
+Cc: Ralf Baechle <ralf@linux-mips.org>
+Cc: <stable@kernel.org>
+---
+ arch/ia64/include/asm/compat.h | 2 +-
+ arch/mips/include/asm/compat.h | 2 +-
+ arch/parisc/include/asm/compat.h | 2 +-
+ arch/powerpc/include/asm/compat.h | 2 +-
+ arch/s390/include/asm/compat.h | 2 +-
+ arch/sparc/include/asm/compat.h | 2 +-
+ arch/x86/include/asm/compat.h | 2 +-
+ include/linux/compat.h | 3 +++
+ kernel/compat.c | 21 +++++++++++++++++++++
+ 10 files changed, 32 insertions(+), 8 deletions(-)
+
+diff --git a/arch/ia64/include/asm/compat.h b/arch/ia64/include/asm/compat.h
+index f90edc8..9301a28 100644
+--- a/arch/ia64/include/asm/compat.h
++++ b/arch/ia64/include/asm/compat.h
+@@ -199,7 +199,7 @@ ptr_to_compat(void __user *uptr)
+ }
+
+ static __inline__ void __user *
+-compat_alloc_user_space (long len)
++arch_compat_alloc_user_space (long len)
+ {
+ struct pt_regs *regs = task_pt_regs(current);
+ return (void __user *) (((regs->r12 & 0xffffffff) & -16) - len);
+diff --git a/arch/mips/include/asm/compat.h b/arch/mips/include/asm/compat.h
+index 613f691..dbc5106 100644
+--- a/arch/mips/include/asm/compat.h
++++ b/arch/mips/include/asm/compat.h
+@@ -145,7 +145,7 @@ static inline compat_uptr_t ptr_to_compat(void __user *uptr)
+ return (u32)(unsigned long)uptr;
+ }
+
+-static inline void __user *compat_alloc_user_space(long len)
++static inline void __user *arch_compat_alloc_user_space(long len)
+ {
+ struct pt_regs *regs = (struct pt_regs *)
+ ((unsigned long) current_thread_info() + THREAD_SIZE - 32) - 1;
+diff --git a/arch/parisc/include/asm/compat.h b/arch/parisc/include/asm/compat.h
+index 02b77ba..efa0b60 100644
+--- a/arch/parisc/include/asm/compat.h
++++ b/arch/parisc/include/asm/compat.h
+@@ -147,7 +147,7 @@ static inline compat_uptr_t ptr_to_compat(void __user *uptr)
+ return (u32)(unsigned long)uptr;
+ }
+
+-static __inline__ void __user *compat_alloc_user_space(long len)
++static __inline__ void __user *arch_compat_alloc_user_space(long len)
+ {
+ struct pt_regs *regs = ¤t->thread.regs;
+ return (void __user *)regs->gr[30];
+diff --git a/arch/powerpc/include/asm/compat.h b/arch/powerpc/include/asm/compat.h
+index 396d21a..a11d4ea 100644
+--- a/arch/powerpc/include/asm/compat.h
++++ b/arch/powerpc/include/asm/compat.h
+@@ -134,7 +134,7 @@ static inline compat_uptr_t ptr_to_compat(void __user *uptr)
+ return (u32)(unsigned long)uptr;
+ }
+
+-static inline void __user *compat_alloc_user_space(long len)
++static inline void __user *arch_compat_alloc_user_space(long len)
+ {
+ struct pt_regs *regs = current->thread.regs;
+ unsigned long usp = regs->gpr[1];
+diff --git a/arch/s390/include/asm/compat.h b/arch/s390/include/asm/compat.h
+index 104f200..a875c2f 100644
+--- a/arch/s390/include/asm/compat.h
++++ b/arch/s390/include/asm/compat.h
+@@ -181,7 +181,7 @@ static inline int is_compat_task(void)
+
+ #endif
+
+-static inline void __user *compat_alloc_user_space(long len)
++static inline void __user *arch_compat_alloc_user_space(long len)
+ {
+ unsigned long stack;
+
+diff --git a/arch/sparc/include/asm/compat.h b/arch/sparc/include/asm/compat.h
+index 5016f76..6f57325 100644
+--- a/arch/sparc/include/asm/compat.h
++++ b/arch/sparc/include/asm/compat.h
+@@ -167,7 +167,7 @@ static inline compat_uptr_t ptr_to_compat(void __user *uptr)
+ return (u32)(unsigned long)uptr;
+ }
+
+-static inline void __user *compat_alloc_user_space(long len)
++static inline void __user *arch_compat_alloc_user_space(long len)
+ {
+ struct pt_regs *regs = current_thread_info()->kregs;
+ unsigned long usp = regs->u_regs[UREG_I6];
+diff --git a/arch/x86/include/asm/compat.h b/arch/x86/include/asm/compat.h
+index 306160e..1d9cd27 100644
+--- a/arch/x86/include/asm/compat.h
++++ b/arch/x86/include/asm/compat.h
+@@ -205,7 +205,7 @@ static inline compat_uptr_t ptr_to_compat(void __user *uptr)
+ return (u32)(unsigned long)uptr;
+ }
+
+-static inline void __user *compat_alloc_user_space(long len)
++static inline void __user *arch_compat_alloc_user_space(long len)
+ {
+ struct pt_regs *regs = task_pt_regs(current);
+ return (void __user *)regs->sp - len;
+diff --git a/include/linux/compat.h b/include/linux/compat.h
+index 9ddc878..5778b55 100644
+--- a/include/linux/compat.h
++++ b/include/linux/compat.h
+@@ -360,5 +360,8 @@ extern ssize_t compat_rw_copy_check_uvector(int type,
+ const struct compat_iovec __user *uvector, unsigned long nr_segs,
+ unsigned long fast_segs, struct iovec *fast_pointer,
+ struct iovec **ret_pointer);
++
++extern void __user *compat_alloc_user_space(unsigned long len);
++
+ #endif /* CONFIG_COMPAT */
+ #endif /* _LINUX_COMPAT_H */
+diff --git a/kernel/compat.c b/kernel/compat.c
+index e167efc..c9e2ec0 100644
+--- a/kernel/compat.c
++++ b/kernel/compat.c
+@@ -1126,3 +1126,24 @@ compat_sys_sysinfo(struct compat_sysinfo __user *info)
+
+ return 0;
+ }
++
++/*
++ * Allocate user-space memory for the duration of a single system call,
++ * in order to marshall parameters inside a compat thunk.
++ */
++void __user *compat_alloc_user_space(unsigned long len)
++{
++ void __user *ptr;
++
++ /* If len would occupy more than half of the entire compat space... */
++ if (unlikely(len > (((compat_uptr_t)~0) >> 1)))
++ return NULL;
++
++ ptr = arch_compat_alloc_user_space(len);
++
++ if (unlikely(!access_ok(VERIFY_WRITE, ptr, len)))
++ return NULL;
++
++ return ptr;
++}
++EXPORT_SYMBOL_GPL(compat_alloc_user_space);
+--
+1.7.3
+