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List:       linux-hardening
Subject:    Re: [PATCH] fs/coda: Do not use partially allocated struct
From:       Jan Harkes <jaharkes () cs ! cmu ! edu>
Date:       2022-05-20 17:11:25
Message-ID: 20220520171125.7u7q4ih5udkykv6b () cs ! cmu ! edu
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Looks good to me.

The old code was trying to be too smart for its own good and the type
gets lost by the uc_data = (void *) cast anyway.

Jan


On Fri, May 20, 2022 at 09:59:22AM -0700, Kees Cook wrote:
> GCC 12 does not like seeing a partially allocated structure being used,
> especially when a pointer is being passed out of function scope. Since
> only the struct coda_in_hdr member of union inputArgs is being allocated
> and used, just replace union inputArgs with struct coda_in_hdr.
> 
> ../fs/coda/upcall.c: In function 'coda_upcall':
> ../fs/coda/upcall.c:801:22: warning: array subscript 'union inputArgs[0]' is partly \
> outside array bounds of 'unsigned char[20]' [-Warray-bounds] 801 |         \
> sig_inputArgs->ih.opcode = CODA_SIGNAL; |                      ^~
> In file included from ../include/linux/fs.h:45,
> from ../include/linux/huge_mm.h:8,
> from ../include/linux/mm.h:700,
> from ../fs/coda/upcall.c:22:
> In function 'kvmalloc',
> inlined from 'kvzalloc' at ../include/linux/slab.h:758:9,
> inlined from 'coda_upcall' at ../fs/coda/upcall.c:794:18:
> ../include/linux/slab.h:750:16: note: object of size 20 allocated by \
> 'kvmalloc_node' 750 |         return kvmalloc_node(size, flags, NUMA_NO_NODE);
> > ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> ../fs/coda/upcall.c: In function 'coda_upcall':
> ../fs/coda/upcall.c:802:22: warning: array subscript 'union inputArgs[0]' is partly \
> outside array bounds of 'unsigned char[20]' [-Warray-bounds] 802 |         \
> sig_inputArgs->ih.unique = req->uc_unique; |                      ^~
> In function 'kvmalloc',
> inlined from 'kvzalloc' at ../include/linux/slab.h:758:9,
> inlined from 'coda_upcall' at ../fs/coda/upcall.c:794:18:
> ../include/linux/slab.h:750:16: note: object of size 20 allocated by \
> 'kvmalloc_node' 750 |         return kvmalloc_node(size, flags, NUMA_NO_NODE);
> > ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> 
> Cc: Jan Harkes <jaharkes@cs.cmu.edu>
> Cc: coda@cs.cmu.edu
> Cc: codalist@coda.cs.cmu.edu
> Signed-off-by: Kees Cook <keescook@chromium.org>
> ---
> fs/coda/upcall.c | 20 ++++++++++----------
> 1 file changed, 10 insertions(+), 10 deletions(-)
> 
> diff --git a/fs/coda/upcall.c b/fs/coda/upcall.c
> index 59f6cfd06f96..21e4f5f446b2 100644
> --- a/fs/coda/upcall.c
> +++ b/fs/coda/upcall.c
> @@ -711,7 +711,7 @@ static int coda_upcall(struct venus_comm *vcp,
> 		       union inputArgs *buffer)
> {
> 	union outputArgs *out;
> -	union inputArgs *sig_inputArgs;
> +	struct coda_in_hdr *ih;
> 	struct upc_req *req = NULL, *sig_req;
> 	int error;
> 
> @@ -791,22 +791,22 @@ static int coda_upcall(struct venus_comm *vcp,
> 	sig_req = kmalloc(sizeof(struct upc_req), GFP_KERNEL);
> 	if (!sig_req) goto exit;
> 
> -	sig_inputArgs = kvzalloc(sizeof(struct coda_in_hdr), GFP_KERNEL);
> -	if (!sig_inputArgs) {
> +	ih = kvzalloc(sizeof(*ih), GFP_KERNEL);
> +	if (!ih) {
> 		kfree(sig_req);
> 		goto exit;
> 	}
> 
> 	error = -EINTR;
> -	sig_inputArgs->ih.opcode = CODA_SIGNAL;
> -	sig_inputArgs->ih.unique = req->uc_unique;
> +	ih->opcode = CODA_SIGNAL;
> +	ih->unique = req->uc_unique;
> 
> 	sig_req->uc_flags = CODA_REQ_ASYNC;
> -	sig_req->uc_opcode = sig_inputArgs->ih.opcode;
> -	sig_req->uc_unique = sig_inputArgs->ih.unique;
> -	sig_req->uc_data = (void *)sig_inputArgs;
> -	sig_req->uc_inSize = sizeof(struct coda_in_hdr);
> -	sig_req->uc_outSize = sizeof(struct coda_in_hdr);
> +	sig_req->uc_opcode = ih->opcode;
> +	sig_req->uc_unique = ih->unique;
> +	sig_req->uc_data = (void *)ih;
> +	sig_req->uc_inSize = sizeof(*ih);
> +	sig_req->uc_outSize = sizeof(*ih);
> 
> 	/* insert at head of queue! */
> 	list_add(&(sig_req->uc_chain), &vcp->vc_pending);
> -- 
> 2.32.0
> 
> 


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