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ETH_MAC indirection erratum

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Pervasive misuse of "ETH_MAC *" (a pointer to an ETH_MAC, aka a 6
element unsigned char array) when a simple "ETH_MAC" is correct.  The
best example of this was eth_mac_fmt() in sim_ether.c with the following
prototype:

    t_stat eth_mac_fmt (ETH_MAC* const mac, char* strmac)

The first parameter is a pointer to an array of 6 unsigned characters,
whereas it really just wants to be a pointer to the first element of the
array:

    t_stat eth_mac_scan (const ETH_MAC mac, char* strmac)

The "ETH_MAC *" indirection error also results in subtle memcpy() and
memcmp() issues, e.g.:

    void network_func(DEVICE *dev, ETH_MAC *mac)
    {
      ETH_MAC other_mac;

      /* ...code... */

      /* memcpy() bug: */
      memcpy(other_mac, mac, sizeof(ETH_MAC));

      /* or worse: */
      memcpy(mac, other_mac, sizeof(ETH_MAC));
    }

eth_copy_mac() and eth_mac_cmp() replace calls to memcpy() and memcmp()
that copy or compare Ethernet MAC addresses. These are type-enforcing
functions, i.e., the parameters are ETH_MAC-s, to avoid the subtle
memcpy() and memcmp() bugs.

This fix solves at least one Heisenbug in _eth_close() while free()-ing
write request buffers (and possibly other Heisenbugs.)
This commit is contained in:
B. Scott Michel
2025-03-03 16:26:28 -08:00
committed by Paul Koning
parent 73e5df3928
commit c20b391eea
10 changed files with 256 additions and 225 deletions
Download Patch File Download Diff File Expand all files Collapse all files

52
sim_ether.h
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@@ -341,22 +341,22 @@ t_stat eth_write (ETH_DEV* dev, ETH_PACK* packet, /* write synchronous pac
int eth_read (ETH_DEV* dev, ETH_PACK* packet, /* read single packet; */
ETH_PCALLBACK routine); /* callback when done*/
t_stat eth_filter (ETH_DEV* dev, int addr_count, /* set filter on incoming packets */
ETH_MAC* const addresses,
const ETH_MAC addresses[],
ETH_BOOL all_multicast,
ETH_BOOL promiscuous);
t_stat eth_filter_hash (ETH_DEV* dev, int addr_count, /* set filter on incoming packets with hash */
ETH_MAC* const addresses,
const ETH_MAC addresses[],
ETH_BOOL all_multicast,
ETH_BOOL promiscuous,
ETH_MULTIHASH* const hash); /* AUTODIN II based 8 byte imperfect hash */
t_stat eth_filter_hash_ex (ETH_DEV* dev, int addr_count,/* set filter on incoming packets with hash */
ETH_MAC* const addresses,
const ETH_MAC addresses[],
ETH_BOOL all_multicast,
ETH_BOOL promiscuous,
ETH_BOOL match_broadcast,
ETH_MULTIHASH* const hash); /* AUTODIN II based 8 byte imperfect hash */
t_stat eth_check_address_conflict (ETH_DEV* dev,
ETH_MAC* const address);
const ETH_MAC address);
const char *eth_version (void); /* Version of dynamically loaded library (pcap) */
void eth_setcrc (ETH_DEV* dev, int need_crc); /* enable/disable CRC mode */
t_stat eth_set_async (ETH_DEV* dev, int latency); /* set read behavior to be async */
@@ -373,9 +373,9 @@ t_stat eth_show_devices (FILE* st, DEVICE *dptr, /* show ethernet devices
int eth_devices (int max, ETH_LIST* dev, ETH_BOOL framers); /* get ethernet devices on host */
void eth_show_dev (FILE*st, ETH_DEV* dev); /* show ethernet device state */
void eth_mac_fmt (ETH_MAC* const add, char* buffer); /* format ethernet mac address */
t_stat eth_mac_scan (ETH_MAC* mac, const char* strmac); /* scan string for mac, put in mac */
t_stat eth_mac_scan_ex (ETH_MAC* mac, /* scan string for mac, put in mac */
void eth_mac_fmt (const ETH_MAC add, char* buffer); /* format ethernet mac address */
t_stat eth_mac_scan (ETH_MAC mac, const char* strmac); /* scan string for mac, put in mac */
t_stat eth_mac_scan_ex (ETH_MAC mac, /* scan string for mac, put in mac */
const char* strmac, UNIT *uptr);/* for specified unit */
t_stat ethq_init (ETH_QUE* que, int max); /* initialize FIFO queue */
@@ -390,6 +390,44 @@ t_stat ethq_destroy(ETH_QUE* que); /* release FIFO queue */
const char *eth_capabilities(void);
t_stat sim_ether_test (DEVICE *dptr, const char *cptr); /* unit test routine */
/* Well-known Ethernet MAC addresses:
*
* eth_mac_any: All zeroes/any address
* eth_mac_bcast: All ones broadcast.
*/
extern const ETH_MAC eth_mac_any;
extern const ETH_MAC eth_mac_bcast;
/* Type-enforcing MAC address copy function.
*
* This inline helps to prevent the following situation:
*
* void network_func(DEVICE *dev, ETH_MAC *mac)
* {
* ETH_MAC other_mac;
*
* ...
* memcpy(other_mac, mac, sizeof(ETH_MAC));
* }
*
* The compiler will happily accept the memcpy() as valid because src and dst are
* converted to "void *". This is a subtle bug -- mac is a pointer to an ETH_MAC
* and memcpy will copy from somewhere other than the first byte of the source MAC
* address.
*/
static inline void eth_copy_mac(ETH_MAC dst, const ETH_MAC src)
{
memcpy(dst, src, sizeof(ETH_MAC));
}
/* Type-enforcing MAC comparison function. Helps to avoid subtle memcmp() issues
* (see above).
*/
static inline int eth_mac_cmp(const ETH_MAC a, const ETH_MAC b)
{
return memcmp(a, b, sizeof(ETH_MAC));
}
#if !defined(SIM_TEST_INIT) /* Need stubs for test APIs */
#define SIM_TEST_INIT
#define SIM_TEST(xxx)