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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: Nicolas Pitre <nico@cam.org>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
This commit is contained in:
Nicolas Pitre 2006-03-25 22:44:05 +00:00 committed by Russell King
parent 0003cedfc5
commit 2ce9804fbd
1 changed files with 1 additions and 1 deletions
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2
arch/arm/kernel/traps.c
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@ -506,7 +506,7 @@ asmlinkage int arm_syscall(int no, struct pt_regs *regs)
if (!pmd_present(*pmd))
goto bad_access;
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);
goto bad_access;
}