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Commit 2ce9804f authored by Nicolas Pitre's avatar Nicolas Pitre Committed by Russell King
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[ARM] 3030/2: fix permission check in the obscur cmpxchg syscall 



Patch from Nicolas Pitre

Quoting RMK:

|pte_write() just says that the page _may_ be writable. It doesn't say
|that the MMU is programmed to allow writes. If pte_dirty() doesn't
|return true, that means that the page is _not_ writable from userspace.
|If you write to it from kernel mode (without using put_user) you'll
|bypass the MMU read-only protection and may end up writing to a page
|owned by two separate processes.

Signed-off-by: default avatarNicolas Pitre <nico@cam.org>
Signed-off-by: default avatarRussell King <rmk+kernel@arm.linux.org.uk>
parent 0003cedf

arch/arm/kernel/traps.c

+1 −1
Original line number Original line Diff line number Diff line
@@ -506,7 +506,7 @@ asmlinkage int arm_syscall(int no, struct pt_regs *regs) 
		if (!pmd_present(*pmd))

		if (!pmd_present(*pmd))

			goto bad_access;

			goto bad_access;

		pte = pte_offset_map_lock(mm, pmd, addr, &ptl);

		pte = pte_offset_map_lock(mm, pmd, addr, &ptl);

		if (!pte_present(*pte) || !pte_write(*pte)) {

		if (!pte_present(*pte) || !pte_dirty(*pte)) {

			pte_unmap_unlock(pte, ptl);

			pte_unmap_unlock(pte, ptl);

			goto bad_access;

			goto bad_access;

		}

		}