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Fix Hash-collision denial-of-service vulnerabilities #796

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Fix Hash-collision denial-of-service vulnerabilities #796

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60 changes: 48 additions & 12 deletions external/sundown/Project/sundown/markdown.c
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Original file line number Diff line number Diff line change
Expand Up @@ -19,12 +19,20 @@

#include "markdown.h"
#include "stack.h"
#include "siphash.h"

#include <assert.h>
#include <string.h>
#include <ctype.h>
#include <stdio.h>

#if __GLIBC__ >= 2 && __GLIBC_MINOR >= 25
#include <sys/random.h>
#else
# define getrandom backport_getrandom
# include <sys/syscall.h>
#endif

#if defined(_WIN32)
#define strncasecmp _strnicmp
#endif
Expand All @@ -50,6 +58,7 @@ struct link_ref {
unsigned int id;

struct buf *link;
struct buf *label;
struct buf *title;

struct link_ref *next;
Expand Down Expand Up @@ -118,10 +127,18 @@ struct sd_markdown {
int in_link_body;
};

int sip_hash_key_init = 0;
uint8_t sip_hash_key[SIP_HASH_KEY_LEN];

/***************************
* HELPER FUNCTIONS *
***************************/

int backport_getrandom(void *buf, size_t buflen, unsigned int flags)
{
return (int)syscall(SYS_getrandom, buf, buflen, flags);
}

static inline struct buf *
rndr_newbuf(struct sd_markdown *rndr, int type)
{
Expand Down Expand Up @@ -170,26 +187,35 @@ unscape_text(struct buf *ob, struct buf *src)
static unsigned int
hash_link_ref(const uint8_t *link_ref, size_t length)
{
size_t i;
unsigned int hash = 0;

for (i = 0; i < length; ++i)
hash = tolower(link_ref[i]) + (hash << 6) + (hash << 16) - hash;

return hash;
return siphash_nocase(link_ref, length, sip_hash_key);
}

static struct link_ref *
add_link_ref(
struct link_ref **references,
const uint8_t *name, size_t name_size)
{
struct link_ref *ref = calloc(1, sizeof(struct link_ref));
unsigned int hash;
struct link_ref *ref;
hash = hash_link_ref(name, name_size);
ref = references[hash % REF_TABLE_SIZE];
while (ref != NULL) {
/* If a reference with the same label exists already, replace it with the new reference */
if (ref->id == hash && ref->label->size == name_size) {
if (strncasecmp((char *)ref->label->data, (char *) name, name_size) == 0) {
bufrelease(ref->label);
bufrelease(ref->link);
bufrelease(ref->title);
return ref;
}
}

ref = ref->next;
}
ref = calloc(1, sizeof(struct link_ref));
if (!ref)
return NULL;

ref->id = hash_link_ref(name, name_size);
ref->id = hash;
ref->next = references[ref->id % REF_TABLE_SIZE];

references[ref->id % REF_TABLE_SIZE] = ref;
Expand All @@ -205,8 +231,11 @@ find_link_ref(struct link_ref **references, uint8_t *name, size_t length)
ref = references[hash % REF_TABLE_SIZE];

while (ref != NULL) {
if (ref->id == hash)
return ref;
if (ref->id == hash && ref->label->size == length) {
if (strncasecmp((char *)ref->label->data, (char *) name, length) == 0) {
return ref;
}
}

ref = ref->next;
}
Expand All @@ -225,6 +254,7 @@ free_link_refs(struct link_ref **references)

while (r) {
next = r->next;
bufrelease(r->label);
bufrelease(r->link);
bufrelease(r->title);
free(r);
Expand Down Expand Up @@ -2408,6 +2438,12 @@ sd_markdown_new(
if (!md)
return NULL;

if (!sip_hash_key_init) {
if (getrandom(sip_hash_key, SIP_HASH_KEY_LEN, 0) < SIP_HASH_KEY_LEN)
return NULL;
sip_hash_key_init = 1;
}

memcpy(&md->cb, callbacks, sizeof(struct sd_callbacks));

stack_init(&md->work_bufs[BUFFER_BLOCK], 4);
Expand Down
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