On 10/18/23 at 08:52am, Andrew Morton wrote:
> On Wed, 18 Oct 2023 23:15:31 +0800 Baoquan He <bhe@xxxxxxxxxx> wrote:
>
> > From: Baoquan He <bhe@xxxxxxxxxx>
> > Date: Wed, 18 Oct 2023 22:50:14 +0800
> > Subject: [PATCH] mm/vmalloc: fix the unchecked dereference warning in vread_iter()
> > Content-type: text/plain
> >
> > LKP reported smatch warning as below:
> >
> > ===================
> > smatch warnings:
> > mm/vmalloc.c:3689 vread_iter() error: we previously assumed 'vm' could be null (see line 3667)
> > ......
> > 06c8994626d1b7 @3667 size = vm ? get_vm_area_size(vm) : va_size(va);
> > ......
> > 06c8994626d1b7 @3689 else if (!(vm->flags & VM_IOREMAP))
> > ^^^^^^^^^
> > Unchecked dereference
> > =====================
> >
> > So add checking on whether 'vm' is not null when dereferencing it in
> > vread_iter(). This mutes smatch complaint.
> >
> > ...
> >
> > --- a/mm/vmalloc.c
> > +++ b/mm/vmalloc.c
> > @@ -3813,7 +3813,7 @@ long vread_iter(struct iov_iter *iter, const char *addr, size_t count)
> >
> > if (flags & VMAP_RAM)
> > copied = vmap_ram_vread_iter(iter, addr, n, flags);
> > - else if (!(vm->flags & VM_IOREMAP))
> > + else if (!(vm && (vm->flags & VM_IOREMAP)))
> > copied = aligned_vread_iter(iter, addr, n);
> > else /* IOREMAP area is treated as memory hole */
> > copied = zero_iter(iter, n);
>
> So is this not a real runtime bug? We're only doing this to suppress a
> smatch warning?
>
> If so, can we please include a description of *why* this wasn't a bug?
> What conditions ensure that vm!=NULL at this point?
I think this is not a real runtime bug. The only chance it can hapen is
when (flags == VMAP_BLOCK) is true. That has been warned and could never
happen. I updated patch log and paste v2 here.
/*
* VMAP_BLOCK indicates a sub-type of vm_map_ram area, need
* be set together with VMAP_RAM.
*/
WARN_ON(flags == VMAP_BLOCK);
if (!vm && !flags)
continue;
>From 89cc02302766ab7a67cc668390c24079b4a9406b Mon Sep 17 00:00:00 2001
From: Baoquan He <bhe@xxxxxxxxxx>
Date: Wed, 18 Oct 2023 22:50:14 +0800
Subject: [PATCH v2] mm/vmalloc: fix the unchecked dereference warning in vread_iter()
Content-type: text/plain
LKP reported smatch warning as below:
===================
smatch warnings:
mm/vmalloc.c:3689 vread_iter() error: we previously assumed 'vm' could be null (see line 3667)
......
06c8994626d1b7 @3667 size = vm ? get_vm_area_size(vm) : va_size(va);
......
06c8994626d1b7 @3689 else if (!(vm->flags & VM_IOREMAP))
^^^^^^^^^
Unchecked dereference
=====================
This is not a real-time bug because the possible null 'vm' in the pointed
place could only happen when flags == VMAP_BLOCK. However, the case
'flags == VMAP_BLOCK' should never happen and has been detected with WARN_ON.
Please check vm_map_ram() implementation and the earlier checking in
vread_iter() at below:
~~~~~~~~~~~~~~~~~~~~~~~~~~
/*
* VMAP_BLOCK indicates a sub-type of vm_map_ram area, need
* be set together with VMAP_RAM.
*/
WARN_ON(flags == VMAP_BLOCK);
if (!vm && !flags)
continue;
~~~~~~~~~~~~~~~~~~~~~~~~~~
So add checking on whether 'vm' could be null when dereferencing it in
vread_iter(). This mutes smatch complaint.
Reported-by: kernel test robot <lkp@xxxxxxxxx>
Reported-by: Dan Carpenter <dan.carpenter@xxxxxxxxxx>
Closes: https://lore.kernel.org/r/202310171600.WCrsOwFj-lkp@xxxxxxxxx/
Signed-off-by: Baoquan He <bhe@xxxxxxxxxx>
---
v1->v2:
- Update patch log to state that it's not a realtime bug as Andrew
suggested.
mm/vmalloc.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/mm/vmalloc.c b/mm/vmalloc.c
index aad48ed8d86b..2cc992392db7 100644
--- a/mm/vmalloc.c
+++ b/mm/vmalloc.c
@@ -3813,7 +3813,7 @@ long vread_iter(struct iov_iter *iter, const char *addr, size_t count)
if (flags & VMAP_RAM)
copied = vmap_ram_vread_iter(iter, addr, n, flags);
- else if (!(vm->flags & VM_IOREMAP))
+ else if (!(vm && (vm->flags & VM_IOREMAP)))
copied = aligned_vread_iter(iter, addr, n);
else /* IOREMAP area is treated as memory hole */
copied = zero_iter(iter, n);
--
2.41.0
