[PATCH 23/23] maccess: return -ERANGE when copy_from_kernel_nofault_allowed fails

[Christoph Hellwig <hch@xxxxxx>]

Allow the callers to distinguish a real unmapped address vs a range
that can't be probed.

Suggested-by: Masami Hiramatsu <mhiramat@xxxxxxxxxx>
Signed-off-by: Christoph Hellwig <hch@xxxxxx>
Reviewed-by: Masami Hiramatsu <mhiramat@xxxxxxxxxx>
---
 mm/maccess.c | 16 +++++++++-------
 1 file changed, 9 insertions(+), 7 deletions(-)

diff --git a/mm/maccess.c b/mm/maccess.c
index 349b6cb14426c..d317f8b8095ca 100644
--- a/mm/maccess.c
+++ b/mm/maccess.c
@@ -25,7 +25,7 @@ bool __weak copy_from_kernel_nofault_allowed(const void *unsafe_src,
 long copy_from_kernel_nofault(void *dst, const void *src, size_t size)
 {
 	if (!copy_from_kernel_nofault_allowed(src, size))
-		return -EFAULT;
+		return -ERANGE;
 
 	pagefault_disable();
 	copy_from_kernel_nofault_loop(dst, src, size, u64, Efault);
@@ -69,7 +69,7 @@ long strncpy_from_kernel_nofault(char *dst, const void *unsafe_addr, long count)
 	if (unlikely(count <= 0))
 		return 0;
 	if (!copy_from_kernel_nofault_allowed(unsafe_addr, count))
-		return -EFAULT;
+		return -ERANGE;
 
 	pagefault_disable();
 	do {
@@ -94,7 +94,8 @@ long strncpy_from_kernel_nofault(char *dst, const void *unsafe_addr, long count)
  * @size: size of the data chunk
  *
  * Safely read from kernel address @src to the buffer at @dst.  If a kernel
- * fault happens, handle that and return -EFAULT.
+ * fault happens, handle that and return -EFAULT.  If @src is not a valid kernel
+ * address, return -ERANGE.
  *
  * We ensure that the copy_from_user is executed in atomic context so that
  * do_page_fault() doesn't attempt to take mmap_sem.  This makes
@@ -107,7 +108,7 @@ long copy_from_kernel_nofault(void *dst, const void *src, size_t size)
 	mm_segment_t old_fs = get_fs();
 
 	if (!copy_from_kernel_nofault_allowed(src, size))
-		return -EFAULT;
+		return -ERANGE;
 
 	set_fs(KERNEL_DS);
 	pagefault_disable();
@@ -159,8 +160,9 @@ long copy_to_kernel_nofault(void *dst, const void *src, size_t size)
  *
  * On success, returns the length of the string INCLUDING the trailing NUL.
  *
- * If access fails, returns -EFAULT (some data may have been copied
- * and the trailing NUL added).
+ * If access fails, returns -EFAULT (some data may have been copied and the
+ * trailing NUL added).  If @unsafe_addr is not a valid kernel address, return
+ * -ERANGE.
  *
  * If @count is smaller than the length of the string, copies @count-1 bytes,
  * sets the last byte of @dst buffer to NUL and returns @count.
@@ -174,7 +176,7 @@ long strncpy_from_kernel_nofault(char *dst, const void *unsafe_addr, long count)
 	if (unlikely(count <= 0))
 		return 0;
 	if (!copy_from_kernel_nofault_allowed(unsafe_addr, count))
-		return -EFAULT;
+		return -ERANGE;
 
 	set_fs(KERNEL_DS);
 	pagefault_disable();
-- 
2.26.2