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* [patch 11/18] mm/usercopy: use memory range to be accessed for wraparound check
@ 2019-08-13 22:37 akpm
  0 siblings, 0 replies; only message in thread
From: akpm @ 2019-08-13 22:37 UTC (permalink / raw)
  To: william.kucharski, tsoni, stable, psodagud, keescook, gregkh,
	isaacm, akpm, mm-commits, torvalds

From: "Isaac J. Manjarres" <isaacm@codeaurora.org>
Subject: mm/usercopy: use memory range to be accessed for wraparound check

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@codeaurora.org>
Signed-off-by: Isaac J. Manjarres <isaacm@codeaurora.org>
Co-developed-by: Prasad Sodagudi <psodagud@codeaurora.org>
Reviewed-by: William Kucharski <william.kucharski@oracle.com>
Acked-by: Kees Cook <keescook@chromium.org>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Trilok Soni <tsoni@codeaurora.org>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

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

--- a/mm/usercopy.c~mm-usercopy-use-memory-range-to-be-accessed-for-wraparound-check
+++ a/mm/usercopy.c
@@ -147,7 +147,7 @@ static inline void check_bogus_address(c
 				       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. */
_

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2019-08-13 22:37 [patch 11/18] mm/usercopy: use memory range to be accessed for wraparound check akpm

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