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udhcpc: check that 4-byte options are indeed 4-byte, closes 11506

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function                                             old     new   delta
udhcp_get_option32                                     -      27     +27
udhcp_get_option                                     231     248     +17
------------------------------------------------------------------------------
(add/remove: 1/0 grow/shrink: 1/0 up/down: 44/0)               Total: 44 bytes

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
This commit is contained in:
Denys Vlasenko
2018-12-17 18:07:18 +01:00
parent 4b72aebe80
commit 6d3b4bb24d
4 changed files with 29 additions and 6 deletions
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19
networking/udhcp/common.c
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@ -272,6 +272,15 @@ uint8_t* FAST_FUNC udhcp_get_option(struct dhcp_packet *packet, int code)
goto complain; /* complain and return NULL */
if (optionptr[OPT_CODE] == code) {
if (optionptr[OPT_LEN] == 0) {
/* So far no valid option with length 0 known.
* Having this check means that searching
* for DHCP_MESSAGE_TYPE need not worry
* that returned pointer might be unsafe
* to dereference.
*/
goto complain; /* complain and return NULL */
}
log_option("option found", optionptr);
return optionptr + OPT_DATA;
}
@ -289,6 +298,16 @@ uint8_t* FAST_FUNC udhcp_get_option(struct dhcp_packet *packet, int code)
return NULL;
}
uint8_t* FAST_FUNC udhcp_get_option32(struct dhcp_packet *packet, int code)
{
uint8_t *r = udhcp_get_option(packet, code);
if (r) {
if (r[-1] != 4)
r = NULL;
}
return r;
}
/* Return the position of the 'end' option (no bounds checking) */
int FAST_FUNC udhcp_end_option(uint8_t *optionptr)
{