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Fix potential race condition

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* src/hsts.c (hsts_read_database): get an open file handle
   instead of a file name.
   (hsts_store_dump): get an open file handle
   instead of a file name.
   (hsts_store_open): open the file and pass the open file handle.
   (hsts_store_save): lock the file before the read-merge-dump
   process.

 Reported-by: Daniel Kahn Gillmor <dkg@fifthhorseman.net>
This commit is contained in:
Ander Juaristi 2015-10-05 23:03:45 +02:00 committed by Tim Rühsen
parent 077e897819
commit f5a63e3100
1 changed files with 67 additions and 57 deletions
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124
src/hsts.c
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@ -39,13 +39,16 @@ as that of the covered work. */
#include "c-ctype.h" #include "c-ctype.h"
#ifdef TESTING #ifdef TESTING
#include "test.h" #include "test.h"
#include <unistd.h> /* for unlink(), used only in tests */
#endif #endif
#include <unistd.h>
#include <sys/types.h>
#include <stdlib.h> #include <stdlib.h>
#include <time.h> #include <time.h>
#include <sys/stat.h> #include <sys/stat.h>
#include <string.h> #include <string.h>
#include <stdio.h>
#include <sys/file.h>
struct hsts_store { struct hsts_store {
struct hash_table *table; struct hash_table *table;
@ -265,9 +268,8 @@ hsts_store_merge (hsts_store_t store,
} }
static bool static bool
hsts_read_database (hsts_store_t store, const char *file, bool merge_with_existing_entries) hsts_read_database (hsts_store_t store, FILE *fp, bool merge_with_existing_entries)
{ {
FILE *fp = NULL;
char *line = NULL, *p; char *line = NULL, *p;
size_t len = 0; size_t len = 0;
int items_read; int items_read;
@ -281,67 +283,54 @@ hsts_read_database (hsts_store_t store, const char *file, bool merge_with_existi
func = (merge_with_existing_entries ? hsts_store_merge : hsts_new_entry); func = (merge_with_existing_entries ? hsts_store_merge : hsts_new_entry);
fp = fopen (file, "r"); while (getline (&line, &len, fp) > 0)
if (fp)
{ {
while (getline (&line, &len, fp) > 0) for (p = line; c_isspace (*p); p++)
{ ;
for (p = line; c_isspace (*p); p++)
;
if (*p == '#') if (*p == '#')
continue; continue;
items_read = sscanf (p, "%255s %d %d %lu %lu", items_read = sscanf (p, "%255s %d %d %lu %lu",
host, host,
&port, &port,
&include_subdomains, &include_subdomains,
(unsigned long *) &created, (unsigned long *) &created,
(unsigned long *) &max_age); (unsigned long *) &max_age);
if (items_read == 5) if (items_read == 5)
func (store, host, port, created, max_age, !!include_subdomains); func (store, host, port, created, max_age, !!include_subdomains);
}
xfree (line);
fclose (fp);
result = true;
} }
xfree (line);
result = true;
return result; return result;
} }
static void static void
hsts_store_dump (hsts_store_t store, const char *filename) hsts_store_dump (hsts_store_t store, FILE *fp)
{ {
FILE *fp = NULL;
hash_table_iterator it; hash_table_iterator it;
fp = fopen (filename, "w"); /* Print preliminary comments. We don't care if any of these fail. */
if (fp) fputs ("# HSTS 1.0 Known Hosts database for GNU Wget.\n", fp);
fputs ("# Edit at your own risk.\n", fp);
fputs ("# <hostname>[:<port>]\t<incl. subdomains>\t<created>\t<max-age>\n", fp);
/* Now cycle through the HSTS store in memory and dump the entries */
for (hash_table_iterate (store->table, &it); hash_table_iter_next (&it);)
{ {
/* Print preliminary comments. We don't care if any of these fail. */ struct hsts_kh *kh = (struct hsts_kh *) it.key;
fputs ("# HSTS 1.0 Known Hosts database for GNU Wget.\n", fp); struct hsts_kh_info *khi = (struct hsts_kh_info *) it.value;
fputs ("# Edit at your own risk.\n", fp);
fputs ("# <hostname>[:<port>]\t<incl. subdomains>\t<created>\t<max-age>\n", fp);
/* Now cycle through the HSTS store in memory and dump the entries */ if (fprintf (fp, "%s\t%d\t%d\t%lu\t%lu\n",
for (hash_table_iterate (store->table, &it); hash_table_iter_next (&it);) kh->host, kh->explicit_port, khi->include_subdomains,
khi->created, khi->max_age) < 0)
{ {
struct hsts_kh *kh = (struct hsts_kh *) it.key; logprintf (LOG_ALWAYS, "Could not write the HSTS database correctly.\n");
struct hsts_kh_info *khi = (struct hsts_kh_info *) it.value; break;
if (fprintf (fp, "%s\t%d\t%d\t%lu\t%lu\n",
kh->host, kh->explicit_port, khi->include_subdomains,
khi->created, khi->max_age) < 0)
{
logprintf (LOG_ALWAYS, "Could not write the HSTS database correctly.\n");
break;
}
} }
fclose (fp);
} }
} }
@ -474,6 +463,7 @@ hsts_store_open (const char *filename)
{ {
hsts_store_t store = NULL; hsts_store_t store = NULL;
struct stat st; struct stat st;
FILE *fp = NULL;
store = xnew0 (struct hsts_store); store = xnew0 (struct hsts_store);
store->table = hash_table_new (0, hsts_hash_func, hsts_cmp_func); store->table = hash_table_new (0, hsts_hash_func, hsts_cmp_func);
@ -484,13 +474,15 @@ hsts_store_open (const char *filename)
if (stat (filename, &st) == 0) if (stat (filename, &st) == 0)
store->last_mtime = st.st_mtime; store->last_mtime = st.st_mtime;
if (!hsts_read_database (store, filename, false)) fp = fopen (filename, "r");
if (!fp || !hsts_read_database (store, fp, false))
{ {
/* abort! */ /* abort! */
hsts_store_close (store); hsts_store_close (store);
xfree (store); xfree (store);
store = NULL;
} }
if (fp)
fclose (fp);
} }
return store; return store;
@ -500,18 +492,36 @@ void
hsts_store_save (hsts_store_t store, const char *filename) hsts_store_save (hsts_store_t store, const char *filename)
{ {
struct stat st; struct stat st;
FILE *fp = NULL;
int fd = 0;
if (filename && hash_table_count (store->table) > 0) if (filename && hash_table_count (store->table) > 0)
{ {
/* If the file has changed, merge the changes with our in-memory data fp = fopen (filename, "a+");
before dumping them to the file. if (fp)
Otherwise we could potentially overwrite the data stored by other Wget processes. {
*/ /* Lock the file to avoid potential race conditions */
if (store->last_mtime && stat (filename, &st) == 0 && st.st_mtime > store->last_mtime) fd = fileno (fp);
hsts_read_database (store, filename, true); flock (fd, LOCK_EX);
/* now dump to the file */ /* If the file has changed, merge the changes with our in-memory data
hsts_store_dump (store, filename); before dumping them to the file.
Otherwise we could potentially overwrite the data stored by other Wget processes.
*/
if (store->last_mtime && stat (filename, &st) == 0 && st.st_mtime > store->last_mtime)
hsts_read_database (store, fp, true);
/* We've merged the latest changes so we can now truncate the file
and dump everything. */
fseek (fp, 0, SEEK_SET);
ftruncate (fd, 0);
/* now dump to the file */
hsts_store_dump (store, fp);
/* fclose is expected to unlock the file for us */
fclose (fp);
}
} }
} }