From: Don Howard <dhoward@redhat.com>
Date: Thu, 16 Sep 2010 22:17:00 -0400
Subject: [misc] make compat_alloc_user_space incorporate access_ok
Message-id: <alpine.LRH.2.00.1009161310420.13835@localhost.localdomain>
Patchwork-id: 28276
O-Subject: [PATCH RHEL5.6 BZ634464] [compat] make compat_alloc_user_space()
	incorporate the access_ok()
Bugzilla: 634464
CVE: CVE-2010-3081
RH-Acked-by: Eugene Teo <eteo@redhat.com>
RH-Acked-by: David S. Miller <davem@redhat.com>
RH-Acked-by: Danny Feng <dfeng@redhat.com>

An exploit for this issue was made public yesterday - this is urgently
needed for 5.5/5.4/5.3 zstreams.  Please review.

Backport of upstream commit:

commit c41d68a513c71e35a14f66d71782d27a79a81ea6
Author: H. Peter Anvin <hpa@linux.intel.com>
Date:   Tue Sep 7 16:16:18 2010 -0700

    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>

Addresses bz 634464, CVE-2010-3081

Signed-off-by: Jarod Wilson <jarod@redhat.com>

diff --git a/include/asm-ia64/compat.h b/include/asm-ia64/compat.h
index 40d01d8..f5ad6a0 100644
--- a/include/asm-ia64/compat.h
+++ b/include/asm-ia64/compat.h
@@ -196,7 +196,7 @@ 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/include/asm-powerpc/compat.h b/include/asm-powerpc/compat.h
index aacaabd..7d48f86 100644
--- a/include/asm-powerpc/compat.h
+++ b/include/asm-powerpc/compat.h
@@ -131,7 +131,7 @@ 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/include/asm-s390/compat.h b/include/asm-s390/compat.h
index 356a0b1..adbdb0a 100644
--- a/include/asm-s390/compat.h
+++ b/include/asm-s390/compat.h
@@ -133,7 +133,7 @@ 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)
 {
 	unsigned long stack;
 
diff --git a/include/asm-x86_64/compat.h b/include/asm-x86_64/compat.h
index b37ab82..8db7242 100644
--- a/include/asm-x86_64/compat.h
+++ b/include/asm-x86_64/compat.h
@@ -196,7 +196,7 @@ 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->rsp - len; 
diff --git a/include/linux/compat.h b/include/linux/compat.h
index eaa41d6..414b35a 100644
--- a/include/linux/compat.h
+++ b/include/linux/compat.h
@@ -235,6 +235,8 @@ static inline int compat_timespec_compare(struct compat_timespec *lhs,
 asmlinkage long compat_sys_adjtimex(struct compat_timex __user *utp);
 
 extern int compat_printk(const char *fmt, ...);
+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 126dee9..95e3a94 100644
--- a/kernel/compat.c
+++ b/kernel/compat.c
@@ -24,6 +24,7 @@
 #include <linux/migrate.h>
 
 #include <asm/uaccess.h>
+#include <linux/module.h>
 
 int get_compat_timespec(struct timespec *ts, const struct compat_timespec __user *cts)
 {
@@ -950,3 +951,24 @@ asmlinkage long compat_sys_move_pages(pid_t pid, unsigned long nr_pages,
 	return sys_move_pages(pid, nr_pages, pages, nodes, status, flags);
 }
 #endif
+
+/*
+ * 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);