linux-kernel - [PATCH 20/20] maccess: return -ERANGE when copy_from_kernel_nofault

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Date:   Tue, 19 May 2020 15:44:49 +0200
From:   Christoph Hellwig <hch@....de>
To:     x86@...nel.org, Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Andrew Morton <akpm@...ux-foundation.org>
Cc:     linux-parisc@...r.kernel.org, linux-um@...ts.infradead.org,
        netdev@...r.kernel.org, bpf@...r.kernel.org, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: [PATCH 20/20] maccess: return -ERANGE when copy_from_kernel_nofault_allowed fails

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

Suggested-by: Masami Hiramatsu <mhiramat@...nel.org>
Signed-off-by: Christoph Hellwig <hch@....de>
---
 mm/maccess.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/mm/maccess.c b/mm/maccess.c
index 1e7d77656c596..4010d64189d21 100644
--- a/mm/maccess.c
+++ b/mm/maccess.c
@@ -25,7 +25,7 @@ bool __weak copy_from_kernel_nofault_allowed(void *dst, const void *unsafe_src,
 long copy_from_kernel_nofault(void *dst, const void *src, size_t size)
 {
 	if (!copy_from_kernel_nofault_allowed(dst, 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(dst, unsafe_addr, count))
-		return -EFAULT;
+		return -ERANGE;
 
 	pagefault_disable();
 	do {
@@ -107,7 +107,7 @@ 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(dst, src, size))
-		return -EFAULT;
+		return -ERANGE;
 
 	set_fs(KERNEL_DS);
 	pagefault_disable();
@@ -174,7 +174,7 @@ 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(dst, unsafe_addr, count))
-		return -EFAULT;
+		return -ERANGE;
 
 	set_fs(KERNEL_DS);
 	pagefault_disable();
-- 
2.26.2