linux-kernel - Re: [PATCH -next] audit: use struct

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Message-ID: <20211214181040.GA13575@embeddedor>
Date:   Tue, 14 Dec 2021 12:10:40 -0600
From:   "Gustavo A. R. Silva" <gustavoars@...nel.org>
To:     Xiu Jianfeng <xiujianfeng@...wei.com>
Cc:     paul@...l-moore.com, eparis@...hat.com, keescook@...omium.org,
        linux-audit@...hat.com, linux-kernel@...r.kernel.org,
        wangweiyang2@...wei.com, linux-hardening@...r.kernel.org,
        "Gustavo A. R. Silva" <gustavoars@...nel.org>
Subject: Re: [PATCH -next] audit: use struct_size() helper in kmalloc()

On Tue, Dec 14, 2021 at 11:54:48AM -0600, Gustavo A. R. Silva wrote:
> On Tue, Dec 14, 2021 at 07:48:54PM +0800, Xiu Jianfeng wrote:
> > Make use of struct_size() helper instead of an open-coded calucation.
> > 
> > Link: https://github.com/KSPP/linux/issues/160
> > Signed-off-by: Xiu Jianfeng <xiujianfeng@...wei.com>
> > ---
> >  kernel/audit.c       | 2 +-
> >  kernel/audit_tree.c  | 2 +-
> >  kernel/auditfilter.c | 2 +-
> >  3 files changed, 3 insertions(+), 3 deletions(-)
> > 
> > diff --git a/kernel/audit.c b/kernel/audit.c
> > index d4084751cfe6..f33028578c60 100644
> > --- a/kernel/audit.c
> > +++ b/kernel/audit.c

This could use struct_size(), too:

1461                 audit_send_reply(skb, seq, AUDIT_SIGNAL_INFO, 0, 0,
1462                                  sig_data, sizeof(*sig_data) + len);

> > @@ -1446,7 +1446,7 @@ static int audit_receive_msg(struct sk_buff *skb, struct nlmsghdr *nlh)
> >  			if (err)
> >  				return err;
> >  		}
> > -		sig_data = kmalloc(sizeof(*sig_data) + len, GFP_KERNEL);
> > +		sig_data = kmalloc(struct_size(sig_data, ctx, len), GFP_KERNEL);
> >  		if (!sig_data) {
> >  			if (audit_sig_sid)
> >  				security_release_secctx(ctx, len);
> > diff --git a/kernel/audit_tree.c b/kernel/audit_tree.c
> > index 72324afcffef..e7315d487163 100644
> > --- a/kernel/audit_tree.c
> > +++ b/kernel/audit_tree.c
> > @@ -94,7 +94,7 @@ static struct audit_tree *alloc_tree(const char *s)
> >  {
> >  	struct audit_tree *tree;
> >  
> > -	tree = kmalloc(sizeof(struct audit_tree) + strlen(s) + 1, GFP_KERNEL);
> > +	tree = kmalloc(struct_size(tree, pathname, strlen(s) + 1), GFP_KERNEL);
> >  	if (tree) {
> >  		refcount_set(&tree->count, 1);
> >  		tree->goner = 0;
> > diff --git a/kernel/auditfilter.c b/kernel/auditfilter.c
> > index 4173e771650c..19352820b274 100644
> > --- a/kernel/auditfilter.c
> > +++ b/kernel/auditfilter.c

Also, in this same file the following piece of code could use
struct_size(), too:

1093                         skb = audit_make_reply(seq, AUDIT_LIST_RULES, 0, 1,
1094                                                data,
1095                                                sizeof(*data) + data->buflen);

Thanks
--
Gustavo

> > @@ -637,7 +637,7 @@ static struct audit_rule_data *audit_krule_to_data(struct audit_krule *krule)
> >  	void *bufp;
> >  	int i;
> >  
> > -	data = kmalloc(sizeof(*data) + krule->buflen, GFP_KERNEL);
> > +	data = kmalloc(struct_size(data, buf, krule->buflen), GFP_KERNEL);
> 
> Why don't you also transform the zero-length array in struct
> audit_rule_data into a flexible-array member:
> 
> 508 struct audit_rule_data {
> 509         __u32           flags;  /* AUDIT_PER_{TASK,CALL}, AUDIT_PREPEND */
> 510         __u32           action; /* AUDIT_NEVER, AUDIT_POSSIBLE, AUDIT_ALWAYS */
> 511         __u32           field_count;
> 512         __u32           mask[AUDIT_BITMASK_SIZE]; /* syscall(s) affected */
> 513         __u32           fields[AUDIT_MAX_FIELDS];
> 514         __u32           values[AUDIT_MAX_FIELDS];
> 515         __u32           fieldflags[AUDIT_MAX_FIELDS];
> 516         __u32           buflen; /* total length of string fields */
> 517         char            buf[0]; /* string fields buffer */
> 518 };
> 
> Thanks
> --
> Gustavo
> 
> >  	if (unlikely(!data))
> >  		return NULL;
> >  	memset(data, 0, sizeof(*data));
> > -- 
> > 2.17.1
> > 
> > 
> > 
> >