RE: [PATCH AUTOSEL 5.3 169/203] x86/platform/uv: Fix kmalloc() NULL check routine

David Laight
2019-10-02T08:34:13Z

From: Sasha Levin
> Sent: 01 October 2019 17:06
> Subject: Re: [PATCH AUTOSEL 5.3 169/203] x86/platform/uv: Fix kmalloc() NULL check routine
>
> On Sun, Sep 22, 2019 at 10:25:44PM +0200, Greg KH wrote:
> >On Sun, Sep 22, 2019 at 02:43:15PM -0400, Sasha Levin wrote:
> >> From: Austin Kim <austindh.kim@gmail.com>
> >>
> >> [ Upstream commit 864b23f0169d5bff677e8443a7a90dfd6b090afc ]
> >>
> >> The result of kmalloc() should have been checked ahead of below statement:
> >>
> >> pqp = (struct bau_pq_entry *)vp;
> >>
> >> Move BUG_ON(!vp) before above statement.
> >>
> >> Signed-off-by: Austin Kim <austindh.kim@gmail.com>
...
> >> ---
> >> arch/x86/platform/uv/tlb_uv.c | 4 ++--
> >> 1 file changed, 2 insertions(+), 2 deletions(-)
> >>
> >> diff --git a/arch/x86/platform/uv/tlb_uv.c b/arch/x86/platform/uv/tlb_uv.c
> >> index 20c389a91b803..5f0a96bf27a1f 100644
> >> --- a/arch/x86/platform/uv/tlb_uv.c
> >> +++ b/arch/x86/platform/uv/tlb_uv.c
> >> @@ -1804,9 +1804,9 @@ static void pq_init(int node, int pnode)
> >>
> >> plsize = (DEST_Q_SIZE + 1) * sizeof(struct bau_pq_entry);
> >> vp = kmalloc_node(plsize, GFP_KERNEL, node);
> >> - pqp = (struct bau_pq_entry *)vp;
> >> - BUG_ON(!pqp);
> >> + BUG_ON(!vp);
> >>
> >> + pqp = (struct bau_pq_entry *)vp;
> >> cp = (char *)pqp + 31;
> >> pqp = (struct bau_pq_entry *)(((unsigned long)cp >> 5) << 5);
> >>
> >
> >How did this even get merged in the first place? I thought a number of
> >us complained about it.
> >
> >This isn't any change in code, and the original is just fine, the author
> >didn't realize how C works :(

Mind you, the code itself if pretty horrid.
Looks like it is aligning to 32 bytes, easier done by:
pqp = (void *)((unsigned long)vp + 31 & ~31);
(and there's a roundup macro to obfuscate it somewhere.)
But I'd also expect to see a matching '+ 31' in the size passed to kmalloc().
Not to mention a comment!

David

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