[PATCH 5.2 010/135] mm/usercopy: use memory range to be accessed for wraparound check

[Sasha Levin]

From: "Isaac J. Manjarres" <isaacm@xxxxxxxxxxxxxx>

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@xxxxxxxxxxxxxx
Fixes: f5509cc18daa ("mm: Hardened usercopy")
Signed-off-by: Prasad Sodagudi <psodagud@xxxxxxxxxxxxxx>
Signed-off-by: Isaac J. Manjarres <isaacm@xxxxxxxxxxxxxx>
Co-developed-by: Prasad Sodagudi <psodagud@xxxxxxxxxxxxxx>
Reviewed-by: William Kucharski <william.kucharski@xxxxxxxxxx>
Acked-by: Kees Cook <keescook@xxxxxxxxxxxx>
Cc: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
Cc: Trilok Soni <tsoni@xxxxxxxxxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
 mm/usercopy.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/mm/usercopy.c b/mm/usercopy.c
index 2a09796edef8d..98e924864554c 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. */
-- 
2.20.1