x86: copy_from_user() should not return -EFAULT

Callers of copy_from_user() expect it to return the number of bytes
it could not copy. In no case it is supposed to return -EFAULT.

In case of a detected buffer overflow just return the requested
length. In addition one could think of a memset that would clear
the size of the target object.

[ hpa: code is not in .32 so not needed for -stable ]

Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Acked-by: Arjan van de Ven <arjan@linux.intel.com>
LKML-Reference: <20100105131911.GC5480@osiris.boeblingen.de.ibm.com>
Signed-off-by: H. Peter Anvin <hpa@zytor.com>

2 files changed, 4 insertions, 6 deletions

diff --git a/arch/x86/include/asm/uaccess_32.h b/arch/x86/include/asm/uaccess_32.h
index 0c9825e97f3..088d09fb161 100644
--- a/arch/x86/include/asm/uaccess_32.h
+++ b/arch/x86/include/asm/uaccess_32.h
@@ -205,14 +205,13 @@ static inline unsigned long __must_check copy_from_user(void *to,
                                           unsigned long n)
 {
         int sz = __compiletime_object_size(to);
-        int ret = -EFAULT;
 
         if (likely(sz == -1 || sz >= n))
-                ret = _copy_from_user(to, from, n);
+                n = _copy_from_user(to, from, n);
         else
                 copy_from_user_overflow();
 
-        return ret;
+        return n;
 }
 
 long __must_check strncpy_from_user(char *dst, const char __user *src,
diff --git a/arch/x86/include/asm/uaccess_64.h b/arch/x86/include/asm/uaccess_64.h
index 46324c6a4f6..535e421498f 100644
--- a/arch/x86/include/asm/uaccess_64.h
+++ b/arch/x86/include/asm/uaccess_64.h
@@ -30,16 +30,15 @@ static inline unsigned long __must_check copy_from_user(void *to,
                                           unsigned long n)
 {
         int sz = __compiletime_object_size(to);
-        int ret = -EFAULT;
 
         might_fault();
         if (likely(sz == -1 || sz >= n))
-                ret = _copy_from_user(to, from, n);
+                n = _copy_from_user(to, from, n);
 #ifdef CONFIG_DEBUG_VM
         else
                 WARN(1, "Buffer overflow detected!\n");
 #endif
-        return ret;
+        return n;
 }
 
 static __always_inline __must_check