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From: "Isaac J. Manjarres" <isaacm@codeaurora.org>
To: keescook@chromium.org, crecklin@redhat.com
Cc: "Isaac J. Manjarres" <isaacm@codeaurora.org>,
	linux-mm@kvack.org, linux-kernel@vger.kernel.org,
	gregkh@linuxfoundation.org, psodagud@codeaurora.org,
	tsoni@codeaurora.org, eberman@codeaurora.org,
	stable@vger.kernel.org
Subject: [PATCH] mm/usercopy: Use memory range to be accessed for wraparound check
Date: Tue, 30 Jul 2019 10:54:13 -0700
Message-ID: <1564509253-23287-1-git-send-email-isaacm@codeaurora.org> (raw)

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.

Fixes: f5509cc18daa ("mm: Hardened usercopy")
Co-developed-by: Prasad Sodagudi <psodagud@codeaurora.org>
Signed-off-by: Prasad Sodagudi <psodagud@codeaurora.org>
Signed-off-by: Isaac J. Manjarres <isaacm@codeaurora.org>
Cc: stable@vger.kernel.org
Reviewed-by: William Kucharski <william.kucharski@oracle.com>
Acked-by: Kees Cook <keescook@chromium.org>
---
 mm/usercopy.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/mm/usercopy.c b/mm/usercopy.c
index 2a09796..98e92486 100644
--- a/mm/usercopy.c
+++ b/mm/usercopy.c
@@ -147,7 +147,7 @@ static inline void check_bogus_address(const unsigned long ptr, unsigned long n,
 				       bool to_user)
 {
 	/* Reject if object wraps past end of memory. */
-	if (ptr + n < ptr)
+	if (ptr + (n - 1) < ptr)
 		usercopy_abort("wrapped address", NULL, to_user, 0, ptr + n);
 
 	/* Reject if NULL or ZERO-allocation. */
-- 
The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum,
a Linux Foundation Collaborative Project


             reply index

Thread overview: 11+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-07-30 17:54 Isaac J. Manjarres [this message]
2019-07-31 20:25 ` Kees Cook
  -- strict thread matches above, loose matches on Subject: below --
2018-11-14  0:51 Isaac J. Manjarres
2018-11-14 10:35 ` William Kucharski
2018-11-14 11:09   ` David Laight
2018-11-14 11:46     ` William Kucharski
2018-11-14 17:32       ` isaacm
2018-11-14 22:50         ` William Kucharski
2018-11-14 23:27   ` Kees Cook
2018-11-14 23:32 ` Kees Cook
2018-11-15  7:05 ` Sasha Levin

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