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netfilter: x_tables: add and use xt_check_entry_offsets 

Currently arp/ip and ip6tables each implement a short helper to check that
the target offset is large enough to hold one xt_entry_target struct and
that t->u.target_size fits within the current rule.

Unfortunately these checks are not sufficient.

To avoid adding new tests to all of ip/ip6/arptables move the current
checks into a helper, then extend this helper in followup patches.

Signed-off-by: Florian Westphal <fw@strlen.de>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
This commit is contained in:
Florian Westphal 2016-04-01 14:17:23 +02:00 committed by Pablo Neira Ayuso
parent 3647234101
commit 7d35812c32
5 changed files with 41 additions and 32 deletions
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4
include/linux/netfilter/x_tables.h
View File

@ -242,6 +242,10 @@ void xt_unregister_match(struct xt_match *target);
int xt_register_matches(struct xt_match *match, unsigned int n);
void xt_unregister_matches(struct xt_match *match, unsigned int n);
int xt_check_entry_offsets(const void *base,
unsigned int target_offset,
unsigned int next_offset);
int xt_check_match(struct xt_mtchk_param *, unsigned int size, u_int8_t proto,
bool inv_proto);
int xt_check_target(struct xt_tgchk_param *, unsigned int size, u_int8_t proto,

11
net/ipv4/netfilter/arp_tables.c
View File

@ -496,19 +496,10 @@ static int mark_source_chains(const struct xt_table_info *newinfo,
static inline int check_entry(const struct arpt_entry *e)
{
const struct xt_entry_target *t;
if (!arp_checkentry(&e->arp))
return -EINVAL;
if (e->target_offset + sizeof(struct xt_entry_target) > e->next_offset)
return -EINVAL;
t = arpt_get_target_c(e);
if (e->target_offset + t->u.target_size > e->next_offset)
return -EINVAL;
return 0;
return xt_check_entry_offsets(e, e->target_offset, e->next_offset);
}
static inline int check_target(struct arpt_entry *e, const char *name)

12
net/ipv4/netfilter/ip_tables.c
View File

@ -590,20 +590,10 @@ static void cleanup_match(struct xt_entry_match *m, struct net *net)
static int
check_entry(const struct ipt_entry *e)
{
const struct xt_entry_target *t;
if (!ip_checkentry(&e->ip))
return -EINVAL;
if (e->target_offset + sizeof(struct xt_entry_target) >
e->next_offset)
return -EINVAL;
t = ipt_get_target_c(e);
if (e->target_offset + t->u.target_size > e->next_offset)
return -EINVAL;
return 0;
return xt_check_entry_offsets(e, e->target_offset, e->next_offset);
}
static int

12
net/ipv6/netfilter/ip6_tables.c
View File

@ -602,20 +602,10 @@ static void cleanup_match(struct xt_entry_match *m, struct net *net)
static int
check_entry(const struct ip6t_entry *e)
{
const struct xt_entry_target *t;
if (!ip6_checkentry(&e->ipv6))
return -EINVAL;
if (e->target_offset + sizeof(struct xt_entry_target) >
e->next_offset)
return -EINVAL;
t = ip6t_get_target_c(e);
if (e->target_offset + t->u.target_size > e->next_offset)
return -EINVAL;
return 0;
return xt_check_entry_offsets(e, e->target_offset, e->next_offset);
}
static int check_match(struct xt_entry_match *m, struct xt_mtchk_param *par)

34
net/netfilter/x_tables.c
View File

@ -541,6 +541,40 @@ int xt_compat_match_to_user(const struct xt_entry_match *m,
EXPORT_SYMBOL_GPL(xt_compat_match_to_user);
#endif /* CONFIG_COMPAT */
/**
* xt_check_entry_offsets - validate arp/ip/ip6t_entry
*
* @base: pointer to arp/ip/ip6t_entry
* @target_offset: the arp/ip/ip6_t->target_offset
* @next_offset: the arp/ip/ip6_t->next_offset
*
* validates that target_offset and next_offset are sane.
*
* The arp/ip/ip6t_entry structure @base must have passed following tests:
* - it must point to a valid memory location
* - base to base + next_offset must be accessible, i.e. not exceed allocated
* length.
*
* Return: 0 on success, negative errno on failure.
*/
int xt_check_entry_offsets(const void *base,
unsigned int target_offset,
unsigned int next_offset)
{
const struct xt_entry_target *t;
const char *e = base;
if (target_offset + sizeof(*t) > next_offset)
return -EINVAL;
t = (void *)(e + target_offset);
if (target_offset + t->u.target_size > next_offset)
return -EINVAL;
return 0;
}
EXPORT_SYMBOL(xt_check_entry_offsets);
int xt_check_target(struct xt_tgchk_param *par,
unsigned int size, u_int8_t proto, bool inv_proto)
{