linux-kernel - Re: [PATCH] ipv4: fib: Fix fib_info_hash

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Message-ID: <20250429052303.88052-1-kuniyu@amazon.com>
Date: Mon, 28 Apr 2025 22:22:56 -0700
From: Kuniyuki Iwashima <kuniyu@...zon.com>
To: <kees@...nel.org>
CC: <davem@...emloft.net>, <dsahern@...nel.org>, <edumazet@...gle.com>,
	<horms@...nel.org>, <kuba@...nel.org>, <kuniyu@...zon.com>,
	<linux-hardening@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
	<netdev@...r.kernel.org>, <pabeni@...hat.com>
Subject: Re: [PATCH] ipv4: fib: Fix fib_info_hash_alloc() allocation type

From: Kees Cook <kees@...nel.org>
Date: Mon, 28 Apr 2025 20:52:59 -0700
> On April 28, 2025 5:43:05 PM PDT, Kuniyuki Iwashima <kuniyu@...zon.com> wrote:
> >Thanks for CC me, David.
> >
> >From: David Ahern <dsahern@...nel.org>
> >Date: Mon, 28 Apr 2025 16:50:53 -0600
> >> On 4/25/25 11:05 PM, Kees Cook wrote:
> >> > In preparation for making the kmalloc family of allocators type aware,
> >> > we need to make sure that the returned type from the allocation matches
> >> > the type of the variable being assigned. (Before, the allocator would
> >> > always return "void *", which can be implicitly cast to any pointer type.)
> >> > 
> >> > This was allocating many sizeof(struct hlist_head *) when it actually
> >> > wanted sizeof(struct hlist_head). Luckily these are the same size.
> >> > Adjust the allocation type to match the assignment.
> >> > 
> >> > Signed-off-by: Kees Cook <kees@...nel.org>
> >> > ---
> >> > Cc: "David S. Miller" <davem@...emloft.net>
> >> > Cc: David Ahern <dsahern@...nel.org>
> >> > Cc: Eric Dumazet <edumazet@...gle.com>
> >> > Cc: Jakub Kicinski <kuba@...nel.org>
> >> > Cc: Paolo Abeni <pabeni@...hat.com>
> >> > Cc: Simon Horman <horms@...nel.org>
> >> > Cc: <netdev@...r.kernel.org>
> >> > ---
> >> >  net/ipv4/fib_semantics.c | 2 +-
> >> >  1 file changed, 1 insertion(+), 1 deletion(-)
> >> > 
> >> > diff --git a/net/ipv4/fib_semantics.c b/net/ipv4/fib_semantics.c
> >> > index f68bb9e34c34..37d12b0bc6be 100644
> >> > --- a/net/ipv4/fib_semantics.c
> >> > +++ b/net/ipv4/fib_semantics.c
> >> > @@ -365,7 +365,7 @@ static struct hlist_head *fib_info_laddrhash_bucket(const struct net *net,
> >> >  static struct hlist_head *fib_info_hash_alloc(unsigned int hash_bits)
> >> >  {
> >> >  	/* The second half is used for prefsrc */
> >> > -	return kvcalloc((1 << hash_bits) * 2, sizeof(struct hlist_head *),
> >> > +	return kvcalloc((1 << hash_bits) * 2, sizeof(struct hlist_head),
> >> >  			GFP_KERNEL);
> >> >  }
> >> >  
> >> 
> >> Reviewed-by: David Ahern <dsahern@...nel.org>
> >> 
> >> Fixes: fa336adc100e ("ipv4: fib: Allocate fib_info_hash[] and
> >> fib_info_laddrhash[] by kvcalloc().)
> >
> >I agree this should target net.git as the last statement
> >will be false with LOCKDEP.
> 
> Which will be false with lockdep? Unless I'm missing it, I think hlist_head is always pointer sized:

Oh sorry, now I'm not sure why I mentioned lockdep...
maybe confused with other code :/



> 
> struct hlist_head {
> 	struct hlist_node *first;
> };