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mm/usercopy: use memory range to be accessed for wraparound check

PATCH In review Kees Cook 2 participants 2 messages Aug 16, 2019

Subsystems (3)
Stable branch Memory management Kernel hardening (not covered by other areas)
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Kees Cook

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PATCH 1/1 mm/usercopy: use memory range to be accessed for wraparound check

From: Prasad Sodagudi <[email protected]>

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/[email protected] open here
Fixes f5509cc18daa ("mm: Hardened usercopy")
Signed-off-by Prasad Sodagudi <[email protected]>
Signed-off-by Isaac J. Manjarres <[email protected]>
Co-developed-by Prasad Sodagudi <[email protected]>
Reviewed-by William Kucharski <[email protected]>
Acked-by Kees Cook <[email protected]>
Cc Greg Kroah-Hartman <[email protected]>
Cc Trilok Soni <[email protected]>
Cc <[email protected]>
Signed-off-by Andrew Morton <[email protected]>
Signed-off-by Linus Torvalds <[email protected]>
[kees: backport to v4.14]
Signed-off-by Kees Cook <[email protected]>
---
 mm/usercopy.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)
mm/usercopy.c +1 -1
index a9852b24715d..975f7dff8059 100644
@@ -121,7 +121,7 @@ static inline const char *check_kernel_text_object(const void *ptr,
 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. */
Signature · 5 lines
2.17.1


-- 
Kees Cook
maintainer
#1 lore raw
Quoted 18 lines · Kees Cook

From: Prasad Sodagudi <[email protected]>

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.

Quoted 14 lines
Link http://lkml.kernel.org/r/[email protected] open here
Fixes f5509cc18daa ("mm: Hardened usercopy")
Signed-off-by Prasad Sodagudi <[email protected]>
Signed-off-by Isaac J. Manjarres <[email protected]>
Co-developed-by Prasad Sodagudi <[email protected]>
Reviewed-by William Kucharski <[email protected]>
Acked-by Kees Cook <[email protected]>
Cc Greg Kroah-Hartman <[email protected]>
Cc Trilok Soni <[email protected]>
Cc <[email protected]>
Signed-off-by Andrew Morton <[email protected]>
Signed-off-by Linus Torvalds <[email protected]>
[kees: backport to v4.14]
Signed-off-by Kees Cook <[email protected]>

This and the 4.9 patch now queued up, thanks for the backports.

greg k-h