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

Christoph Hellwig
2020-05-21T15:24:20Z

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

Suggested-by: Masami Hiramatsu <mhiramat@kernel.org>
Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Masami Hiramatsu <mhiramat@kernel.org>
---
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