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[EBTABLES]: Fix wraparounds in ebt_entries verification.

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We need to verify that
	a) we are not too close to the end of buffer to dereference
	b) next entry we'll be checking won't be _before_ our

While we are at it, don't subtract unrelated pointers...

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Al Viro 2006-11-30 19:22:42 -08:00 committed by David S. Miller
parent b6332e6cf9
commit bb2ef25c2c
1 changed files with 16 additions and 7 deletions
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23
net/bridge/netfilter/ebtables.c
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@ -401,13 +401,17 @@ ebt_check_entry_size_and_hooks(struct ebt_entry *e,
struct ebt_entries **hook_entries, unsigned int *n, unsigned int *cnt,
unsigned int *totalcnt, unsigned int *udc_cnt, unsigned int valid_hooks)
{
unsigned int offset = (char *)e - newinfo->entries;
size_t left = (limit - base) - offset;
int i;
if (left < sizeof(unsigned int))
goto Esmall;
for (i = 0; i < NF_BR_NUMHOOKS; i++) {
if ((valid_hooks & (1 << i)) == 0)
continue;
if ( (char *)hook_entries[i] - base ==
(char *)e - newinfo->entries)
if ((char *)hook_entries[i] == base + offset)
break;
}
/* beginning of a new chain
@ -428,11 +432,8 @@ ebt_check_entry_size_and_hooks(struct ebt_entry *e,
return -EINVAL;
}
/* before we look at the struct, be sure it is not too big */
if ((char *)hook_entries[i] + sizeof(struct ebt_entries)
> limit) {
BUGPRINT("entries_size too small\n");
return -EINVAL;
}
if (left < sizeof(struct ebt_entries))
goto Esmall;
if (((struct ebt_entries *)e)->policy != EBT_DROP &&
((struct ebt_entries *)e)->policy != EBT_ACCEPT) {
/* only RETURN from udc */
@ -455,6 +456,8 @@ ebt_check_entry_size_and_hooks(struct ebt_entry *e,
return 0;
}
/* a plain old entry, heh */
if (left < sizeof(struct ebt_entry))
goto Esmall;
if (sizeof(struct ebt_entry) > e->watchers_offset ||
e->watchers_offset > e->target_offset ||
e->target_offset >= e->next_offset) {
@ -466,10 +469,16 @@ ebt_check_entry_size_and_hooks(struct ebt_entry *e,
BUGPRINT("target size too small\n");
return -EINVAL;
}
if (left < e->next_offset)
goto Esmall;
(*cnt)++;
(*totalcnt)++;
return 0;
Esmall:
BUGPRINT("entries_size too small\n");
return -EINVAL;
}
struct ebt_cl_stack