mm: vmalloc: avoid racy handling of debugobjects in vunmap

Currently, __vunmap flow is,
 1) Release the VM area
 2) Free the debug objects corresponding to that vm area.

This leave some race window open.
 1) Release the VM area
 1.5) Some other client gets the same vm area
 1.6) This client allocates new debug objects on the same
      vm area
 2) Free the debug objects corresponding to this vm area.

Here, we actually free 'other' client's debug objects.

Fix this by freeing the debug objects first and then releasing the VM
area.

Link: http://lkml.kernel.org/r/1523961828-9485-2-git-send-email-cpandya@codeaurora.org
Signed-off-by: Chintan Pandya <cpandya@codeaurora.org>
Reviewed-by: Andrew Morton <akpm@linux-foundation.org>
Cc: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Cc: Byungchul Park <byungchul.park@lge.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Florian Fainelli <f.fainelli@gmail.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Laura Abbott <labbott@redhat.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: Wei Yang <richard.weiyang@gmail.com>
Cc: Yisheng Xie <xieyisheng1@huawei.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/mm/vmalloc.c b/mm/vmalloc.c
index 12bd82e6554ecfb2333507a8d09c39509198ef18..4df66e1abeb15ab4773605e13bb918d01309a1d2 100644 (file)
--- a/mm/vmalloc.c
+++ b/mm/vmalloc.c
@@ -1504,7 +1504,7 @@ static void __vunmap(const void *addr, int deallocate_pages)
                        addr))
                return;
 
-       area = remove_vm_area(addr);
+       area = find_vmap_area((unsigned long)addr)->vm;
        if (unlikely(!area)) {
                WARN(1, KERN_ERR "Trying to vfree() nonexistent vm area (%p)\n",
                                addr);
@@ -1514,6 +1514,7 @@ static void __vunmap(const void *addr, int deallocate_pages)
        debug_check_no_locks_freed(addr, get_vm_area_size(area));
        debug_check_no_obj_freed(addr, get_vm_area_size(area));
 
+       remove_vm_area(addr);
        if (deallocate_pages) {
                int i;