linux-kernel - [PATCH 4.9 043/103] mm/usercopy: use memory range to be accessed for wraparound check

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Message-Id: <20190822171730.551985628@linuxfoundation.org>
Date:   Thu, 22 Aug 2019 10:18:31 -0700
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Prasad Sodagudi <psodagud@...eaurora.org>,
        "Isaac J. Manjarres" <isaacm@...eaurora.org>,
        William Kucharski <william.kucharski@...cle.com>,
        Kees Cook <keescook@...omium.org>,
        Trilok Soni <tsoni@...eaurora.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>
Subject: [PATCH 4.9 043/103] mm/usercopy: use memory range to be accessed for wraparound check

From: Isaac J. Manjarres <isaacm@...eaurora.org>

commit 951531691c4bcaa59f56a316e018bc2ff1ddf855 upstream.

Currently, when checking to see if accessing n bytes starting at address
"ptr" will cause a wraparound in the memory addresses, the check in
check_bogus_address() adds an extra byte, which is incorrect, as the
range of addresses that will be accessed is [ptr, ptr + (n - 1)].

This can lead to incorrectly detecting a wraparound in the memory
address, when trying to read 4 KB from memory that is mapped to the the
last possible page in the virtual address space, when in fact, accessing
that range of memory would not cause a wraparound to occur.

Use the memory range that will actually be accessed when considering if
accessing a certain amount of bytes will cause the memory address to
wrap around.

Link: http://lkml.kernel.org/r/1564509253-23287-1-git-send-email-isaacm@codeaurora.org
Fixes: f5509cc18daa ("mm: Hardened usercopy")
Signed-off-by: Prasad Sodagudi <psodagud@...eaurora.org>
Signed-off-by: Isaac J. Manjarres <isaacm@...eaurora.org>
Co-developed-by: Prasad Sodagudi <psodagud@...eaurora.org>
Reviewed-by: William Kucharski <william.kucharski@...cle.com>
Acked-by: Kees Cook <keescook@...omium.org>
Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc: Trilok Soni <tsoni@...eaurora.org>
Cc: <stable@...r.kernel.org>
Signed-off-by: Andrew Morton <akpm@...ux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@...ux-foundation.org>
[kees: backport to v4.9]
Signed-off-by: Kees Cook <keescook@...omium.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 mm/usercopy.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/mm/usercopy.c
+++ b/mm/usercopy.c
@@ -124,7 +124,7 @@ static inline const char *check_kernel_t
 static inline const char *check_bogus_address(const void *ptr, unsigned long n)
 {
 	/* Reject if object wraps past end of memory. */
-	if ((unsigned long)ptr + n < (unsigned long)ptr)
+	if ((unsigned long)ptr + (n - 1) < (unsigned long)ptr)
 		return "<wrapped address>";

 	/* Reject if NULL or ZERO-allocation. */