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netfilter: x_tables: check for bogus target offset 

We're currently asserting that targetoff + targetsize <= nextoff.

Extend it to also check that targetoff is >= sizeof(xt_entry).
Since this is generic code, add an argument pointing to the start of the
match/target, we can then derive the base structure size from the delta.

We also need the e->elems pointer in a followup change to validate matches.

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 14:17:28 +02:00 committed by Pablo Neira Ayuso
parent 7ed2abddd2
commit ce683e5f9d
5 changed files with 26 additions and 10 deletions
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4
include/linux/netfilter/x_tables.h
View File

@ -242,7 +242,7 @@ 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,
int xt_check_entry_offsets(const void *base, const char *elems,
unsigned int target_offset,
unsigned int next_offset);
@ -494,7 +494,7 @@ void xt_compat_target_from_user(struct xt_entry_target *t, void **dstptr,
unsigned int *size);
int xt_compat_target_to_user(const struct xt_entry_target *t,
void __user **dstptr, unsigned int *size);
int xt_compat_check_entry_offsets(const void *base,
int xt_compat_check_entry_offsets(const void *base, const char *elems,
unsigned int target_offset,
unsigned int next_offset);

5
net/ipv4/netfilter/arp_tables.c
View File

@ -592,7 +592,8 @@ static inline int check_entry_size_and_hooks(struct arpt_entry *e,
if (!arp_checkentry(&e->arp))
return -EINVAL;
err = xt_check_entry_offsets(e, e->target_offset, e->next_offset);
err = xt_check_entry_offsets(e, e->elems, e->target_offset,
e->next_offset);
if (err)
return err;
@ -1254,7 +1255,7 @@ check_compat_entry_size_and_hooks(struct compat_arpt_entry *e,
if (!arp_checkentry(&e->arp))
return -EINVAL;
ret = xt_compat_check_entry_offsets(e, e->target_offset,
ret = xt_compat_check_entry_offsets(e, e->elems, e->target_offset,
e->next_offset);
if (ret)
return ret;

5
net/ipv4/netfilter/ip_tables.c
View File

@ -754,7 +754,8 @@ check_entry_size_and_hooks(struct ipt_entry *e,
if (!ip_checkentry(&e->ip))
return -EINVAL;
err = xt_check_entry_offsets(e, e->target_offset, e->next_offset);
err = xt_check_entry_offsets(e, e->elems, e->target_offset,
e->next_offset);
if (err)
return err;
@ -1513,7 +1514,7 @@ check_compat_entry_size_and_hooks(struct compat_ipt_entry *e,
if (!ip_checkentry(&e->ip))
return -EINVAL;
ret = xt_compat_check_entry_offsets(e,
ret = xt_compat_check_entry_offsets(e, e->elems,
e->target_offset, e->next_offset);
if (ret)
return ret;

5
net/ipv6/netfilter/ip6_tables.c
View File

@ -766,7 +766,8 @@ check_entry_size_and_hooks(struct ip6t_entry *e,
if (!ip6_checkentry(&e->ipv6))
return -EINVAL;
err = xt_check_entry_offsets(e, e->target_offset, e->next_offset);
err = xt_check_entry_offsets(e, e->elems, e->target_offset,
e->next_offset);
if (err)
return err;
@ -1525,7 +1526,7 @@ check_compat_entry_size_and_hooks(struct compat_ip6t_entry *e,
if (!ip6_checkentry(&e->ipv6))
return -EINVAL;
ret = xt_compat_check_entry_offsets(e,
ret = xt_compat_check_entry_offsets(e, e->elems,
e->target_offset, e->next_offset);
if (ret)
return ret;

17
net/netfilter/x_tables.c
View File

@ -546,14 +546,17 @@ struct compat_xt_standard_target {
compat_uint_t verdict;
};
/* see xt_check_entry_offsets */
int xt_compat_check_entry_offsets(const void *base,
int xt_compat_check_entry_offsets(const void *base, const char *elems,
unsigned int target_offset,
unsigned int next_offset)
{
long size_of_base_struct = elems - (const char *)base;
const struct compat_xt_entry_target *t;
const char *e = base;
if (target_offset < size_of_base_struct)
return -EINVAL;
if (target_offset + sizeof(*t) > next_offset)
return -EINVAL;
@ -577,12 +580,16 @@ EXPORT_SYMBOL(xt_compat_check_entry_offsets);
* xt_check_entry_offsets - validate arp/ip/ip6t_entry
*
* @base: pointer to arp/ip/ip6t_entry
* @elems: pointer to first xt_entry_match, i.e. ip(6)t_entry->elems
* @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.
* Also see xt_compat_check_entry_offsets for CONFIG_COMPAT version.
*
* This function does not validate the targets or matches themselves, it
* only tests that all the offsets and sizes are correct.
*
* 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
@ -591,12 +598,18 @@ EXPORT_SYMBOL(xt_compat_check_entry_offsets);
* Return: 0 on success, negative errno on failure.
*/
int xt_check_entry_offsets(const void *base,
const char *elems,
unsigned int target_offset,
unsigned int next_offset)
{
long size_of_base_struct = elems - (const char *)base;
const struct xt_entry_target *t;
const char *e = base;
/* target start is within the ip/ip6/arpt_entry struct */
if (target_offset < size_of_base_struct)
return -EINVAL;
if (target_offset + sizeof(*t) > next_offset)
return -EINVAL;