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Switch make_safe_url() to more efficient implementation.

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Contributed by: Bert Gijsbers
This commit is contained in:
Emil Mikulic 2018-12-09 23:18:00 +11:00
parent 5f519fec8d
commit bdae96c653
1 changed files with 43 additions and 99 deletions
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142
darkhttpd.c
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@ -481,118 +481,62 @@ static char *split_string(const char *src,
return dest;
}
/* Consolidate slashes in-place by shifting parts of the string over repeated
* slashes.
*/
static void consolidate_slashes(char *s) {
size_t left = 0, right = 0;
int saw_slash = 0;
assert(s != NULL);
while (s[right] != '\0') {
if (saw_slash) {
if (s[right] == '/')
right++;
else {
saw_slash = 0;
s[left++] = s[right++];
}
} else {
if (s[right] == '/')
saw_slash++;
s[left++] = s[right++];
}
}
s[left] = '\0';
}
/* Resolve /./ and /../ in a URL, in-place. Also strip out query params.
* Returns NULL if the URL is invalid/unsafe, or the original buffer if
* successful.
*/
static char *make_safe_url(char *url) {
struct {
char *start;
size_t len;
} *chunks;
unsigned int num_slashes, num_chunks;
size_t urllen, i, j, pos;
int ends_in_slash;
static char *make_safe_url(char *const url) {
char *src = url, *dst;
#define ends(c) ((c) == '/' || (c) == '\0')
/* strip query params */
for (pos=0; url[pos] != '\0'; pos++) {
if (url[pos] == '?') {
url[pos] = '\0';
/* URLs not starting with a slash are illegal. */
if (*src != '/')
return NULL;
/* Fast case: skip until first double-slash or dot-dir. */
for ( ; *src && *src != '?'; ++src) {
if (*src == '/') {
if (src[1] == '/')
break;
else if (src[1] == '.') {
if (ends(src[2]))
break;
else if (src[2] == '.' && ends(src[3]))
break;
}
}
}
if (url[0] != '/')
return NULL;
consolidate_slashes(url);
urllen = strlen(url);
if (urllen > 0)
ends_in_slash = (url[urllen-1] == '/');
else
ends_in_slash = 1;
/* count the slashes */
for (i=0, num_slashes=0; i < urllen; i++)
if (url[i] == '/')
num_slashes++;
/* make an array for the URL elements */
assert(num_slashes > 0);
chunks = xmalloc(sizeof(*chunks) * num_slashes);
/* split by slashes and build chunks array */
num_chunks = 0;
for (i=1; i<urllen;) {
/* look for the next slash */
for (j=i; j<urllen && url[j] != '/'; j++)
/* Copy to dst, while collapsing multi-slashes and handling dot-dirs. */
dst = src;
while (*src && *src != '?') {
if (*src != '/')
*dst++ = *src++;
else if (*++src == '/')
;
/* process url[i,j) */
if ((j == i+1) && (url[i] == '.'))
/* "." */;
else if ((j == i+2) && (url[i] == '.') && (url[i+1] == '.')) {
/* ".." */
if (num_chunks == 0) {
/* unsafe string so free chunks */
free(chunks);
return (NULL);
} else
num_chunks--;
} else {
chunks[num_chunks].start = url+i;
chunks[num_chunks].len = j-i;
num_chunks++;
else if (*src != '.')
*dst++ = '/';
else if (ends(src[1]))
/* Ignore single-dot component. */
++src;
else if (src[1] == '.' && ends(src[2])) {
/* Double-dot component. */
src += 2;
if (dst == url)
return NULL; /* Illegal URL */
else
/* Backtrack to previous slash. */
while (*--dst != '/' && dst > url);
}
else
*dst++ = '/';
}
i = j + 1; /* url[j] is a slash - move along one */
}
/* reassemble in-place */
pos = 0;
for (i=0; i<num_chunks; i++) {
assert(pos <= urllen);
url[pos++] = '/';
assert(pos + chunks[i].len <= urllen);
assert(url + pos <= chunks[i].start);
if (url+pos < chunks[i].start)
memmove(url+pos, chunks[i].start, chunks[i].len);
pos += chunks[i].len;
}
free(chunks);
if ((num_chunks == 0) || ends_in_slash)
url[pos++] = '/';
assert(pos <= urllen);
url[pos] = '\0';
if (dst == url)
++dst;
*dst = '\0';
return url;
#undef ends
}
static void add_forward_mapping(const char * const host,