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Added disable_symlinks directive.

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To completely disable symlinks (disable_symlinks on)
we use openat(O_NOFOLLOW) for each path component
to avoid races.

To allow symlinks with the same owner (disable_symlinks if_not_owner),
use openat() (followed by fstat()) and fstatat(AT_SYMLINK_NOFOLLOW),
and then compare uids between fstat() and fstatat().

As there is a race between openat() and fstatat() we don't
know if openat() in fact opened symlink or not.  Therefore,
we have to compare uids even if fstatat() reports the opened
component isn't a symlink (as we don't know whether it was
symlink during openat() or not).

Default value is off, i.e. symlinks are allowed.
This commit is contained in:
Andrey Belov 2012-02-13 16:29:04 +00:00
parent 32c8df44d5
commit bd1e719bf9
5 changed files with 294 additions and 24 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

5
src/core/ngx_core.h
View File

@ -91,5 +91,10 @@ typedef void (*ngx_connection_handler_pt)(ngx_connection_t *c);
void ngx_cpuinfo(void);
#if (NGX_HAVE_OPENAT)
#define NGX_DISABLE_SYMLINKS_OFF 0
#define NGX_DISABLE_SYMLINKS_ON 1
#define NGX_DISABLE_SYMLINKS_NOTOWNER 2
#endif
#endif /* _NGX_CORE_H_INCLUDED_ */

266
src/core/ngx_open_file_cache.c
View File

@ -22,6 +22,15 @@
static void ngx_open_file_cache_cleanup(void *data);
#if (NGX_HAVE_OPENAT)
static ngx_fd_t ngx_openat_file_owner(ngx_fd_t at_fd, const u_char *name,
ngx_int_t mode, ngx_int_t create, ngx_int_t access);
#endif
static ngx_fd_t ngx_open_file_wrapper(ngx_str_t *name,
ngx_open_file_info_t *of, ngx_int_t mode, ngx_int_t create,
ngx_int_t access);
static ngx_int_t ngx_file_info_wrapper(ngx_str_t *name,
ngx_open_file_info_t *of, ngx_file_info_t *fi);
static ngx_int_t ngx_open_and_stat_file(ngx_str_t *name,
ngx_open_file_info_t *of, ngx_log_t *log);
static void ngx_open_file_add_event(ngx_open_file_cache_t *cache,
@ -147,9 +156,7 @@ ngx_open_cached_file(ngx_open_file_cache_t *cache, ngx_str_t *name,
if (of->test_only) {
if (ngx_file_info(name->data, &fi) == NGX_FILE_ERROR) {
of->err = ngx_errno;
of->failed = ngx_file_info_n;
if (ngx_file_info_wrapper(name, of, &fi) == NGX_FILE_ERROR) {
return NGX_ERROR;
}
@ -217,7 +224,11 @@ ngx_open_cached_file(ngx_open_file_cache_t *cache, ngx_str_t *name,
if (file->use_event
|| (file->event == NULL
&& (of->uniq == 0 || of->uniq == file->uniq)
&& now - file->created < of->valid))
&& now - file->created < of->valid
#if (NGX_HAVE_OPENAT)
&& of->disable_symlinks == file->disable_symlinks
#endif
))
{
if (file->err == 0) {
@ -239,7 +250,12 @@ ngx_open_cached_file(ngx_open_file_cache_t *cache, ngx_str_t *name,
} else {
of->err = file->err;
#if (NGX_HAVE_OPENAT)
of->failed = file->disable_symlinks ? ngx_openat_file_n
: ngx_open_file_n;
#else
of->failed = ngx_open_file_n;
#endif
}
goto found;
@ -375,6 +391,9 @@ update:
file->fd = of->fd;
file->err = of->err;
#if (NGX_HAVE_OPENAT)
file->disable_symlinks = of->disable_symlinks;
#endif
if (of->err == 0) {
file->uniq = of->uniq;
@ -459,6 +478,212 @@ failed:
}
#if (NGX_HAVE_OPENAT)
static ngx_fd_t
ngx_openat_file_owner(ngx_fd_t at_fd, const u_char *name,
ngx_int_t mode, ngx_int_t create, ngx_int_t access)
{
ngx_fd_t fd;
ngx_file_info_t fi, atfi;
/*
* To allow symlinks with the same owner, use openat() (followed
* by fstat()) and fstatat(AT_SYMLINK_NOFOLLOW), and then compare
* uids between fstat() and fstatat().
*
* As there is a race between openat() and fstatat() we don't
* know if openat() in fact opened symlink or not. Therefore,
* we have to compare uids even if fstatat() reports the opened
* component isn't a symlink (as we don't know whether it was
* symlink during openat() or not).
*/
fd = ngx_openat_file(at_fd, name, mode, create, access);
if (fd == NGX_FILE_ERROR) {
return NGX_FILE_ERROR;
}
if (ngx_file_at_info(at_fd, name, &atfi, AT_SYMLINK_NOFOLLOW)
== NGX_FILE_ERROR)
{
ngx_close_file(fd);
return NGX_FILE_ERROR;
}
if (ngx_fd_info(fd, &fi) == NGX_FILE_ERROR) {
ngx_close_file(fd);
return NGX_FILE_ERROR;
}
if (fi.st_uid != atfi.st_uid) {
ngx_close_file(fd);
ngx_set_errno(NGX_ELOOP);
return NGX_FILE_ERROR;
}
return fd;
}
#endif
static ngx_fd_t
ngx_open_file_wrapper(ngx_str_t *name, ngx_open_file_info_t *of,
ngx_int_t mode, ngx_int_t create, ngx_int_t access)
{
ngx_fd_t fd;
#if !(NGX_HAVE_OPENAT)
fd = ngx_open_file(name->data, mode, create, access);
if (fd == NGX_FILE_ERROR) {
of->err = ngx_errno;
of->failed = ngx_open_file_n;
return NGX_FILE_ERROR;
}
return fd;
#else
u_char *p, *cp, *end;
ngx_fd_t at_fd;
if (of->disable_symlinks == NGX_DISABLE_SYMLINKS_OFF) {
fd = ngx_open_file(name->data, mode, create, access);
if (fd == NGX_FILE_ERROR) {
of->err = ngx_errno;
of->failed = ngx_open_file_n;
return NGX_FILE_ERROR;
}
return fd;
}
at_fd = ngx_openat_file(AT_FDCWD, "/", NGX_FILE_RDONLY|NGX_FILE_NONBLOCK,
NGX_FILE_OPEN, 0);
if (at_fd == NGX_FILE_ERROR) {
of->err = ngx_errno;
of->failed = ngx_openat_file_n;
return NGX_FILE_ERROR;
}
end = name->data + name->len;
p = name->data + 1;
for ( ;; ) {
cp = ngx_strlchr(p, end, '/');
if (cp == NULL) {
break;
}
*cp = '\0';
if (of->disable_symlinks == NGX_DISABLE_SYMLINKS_NOTOWNER) {
fd = ngx_openat_file_owner(at_fd, p,
NGX_FILE_RDONLY|NGX_FILE_NONBLOCK,
NGX_FILE_OPEN, 0);
} else {
fd = ngx_openat_file(at_fd, p,
NGX_FILE_RDONLY|NGX_FILE_NONBLOCK|NGX_FILE_NOFOLLOW,
NGX_FILE_OPEN, 0);
}
*cp = '/';
ngx_close_file(at_fd);
if (fd == NGX_FILE_ERROR) {
of->err = ngx_errno;
of->failed = ngx_openat_file_n;
return NGX_FILE_ERROR;
}
p = cp + 1;
at_fd = fd;
}
if (of->disable_symlinks == NGX_DISABLE_SYMLINKS_NOTOWNER) {
fd = ngx_openat_file_owner(at_fd, p, mode, create, access);
} else {
fd = ngx_openat_file(at_fd, p, mode|NGX_FILE_NOFOLLOW, create, access);
}
if (fd == NGX_FILE_ERROR) {
of->err = ngx_errno;
of->failed = ngx_openat_file_n;
}
ngx_close_file(at_fd);
return fd;
#endif
}
static ngx_int_t
ngx_file_info_wrapper(ngx_str_t *name, ngx_open_file_info_t *of,
ngx_file_info_t *fi)
{
ngx_int_t rc;
#if !(NGX_HAVE_OPENAT)
rc = ngx_file_info(name->data, fi);
if (rc == NGX_FILE_ERROR) {
of->err = ngx_errno;
of->failed = ngx_file_info_n;
return NGX_FILE_ERROR;
}
return rc;
#else
ngx_fd_t fd;
if (of->disable_symlinks == NGX_DISABLE_SYMLINKS_OFF) {
rc = ngx_file_info(name->data, fi);
if (rc == NGX_FILE_ERROR) {
of->err = ngx_errno;
of->failed = ngx_file_info_n;
return NGX_FILE_ERROR;
}
return rc;
}
fd = ngx_open_file_wrapper(name, of, NGX_FILE_RDONLY|NGX_FILE_NONBLOCK,
NGX_FILE_OPEN, 0);
if (fd == NGX_FILE_ERROR) {
return NGX_FILE_ERROR;
}
if (ngx_fd_info(fd, fi) == NGX_FILE_ERROR) {
of->err = ngx_errno;
of->failed = ngx_fd_info_n;
ngx_close_file(fd);
return NGX_FILE_ERROR;
}
ngx_close_file(fd);
return NGX_OK;
#endif
}
static ngx_int_t
ngx_open_and_stat_file(ngx_str_t *name, ngx_open_file_info_t *of,
ngx_log_t *log)
@ -468,9 +693,9 @@ ngx_open_and_stat_file(ngx_str_t *name, ngx_open_file_info_t *of,
if (of->fd != NGX_INVALID_FILE) {
if (ngx_file_info(name->data, &fi) == NGX_FILE_ERROR) {
of->failed = ngx_file_info_n;
goto failed;
if (ngx_file_info_wrapper(name, of, &fi) == NGX_FILE_ERROR) {
of->fd = NGX_INVALID_FILE;
return NGX_ERROR;
}
if (of->uniq == ngx_file_uniq(&fi)) {
@ -479,9 +704,9 @@ ngx_open_and_stat_file(ngx_str_t *name, ngx_open_file_info_t *of,
} else if (of->test_dir) {
if (ngx_file_info(name->data, &fi) == NGX_FILE_ERROR) {
of->failed = ngx_file_info_n;
goto failed;
if (ngx_file_info_wrapper(name, of, &fi) == NGX_FILE_ERROR) {
of->fd = NGX_INVALID_FILE;
return NGX_ERROR;
}
if (ngx_is_dir(&fi)) {
@ -496,18 +721,18 @@ ngx_open_and_stat_file(ngx_str_t *name, ngx_open_file_info_t *of,
* This flag has no effect on a regular files.
*/
fd = ngx_open_file(name->data, NGX_FILE_RDONLY|NGX_FILE_NONBLOCK,
NGX_FILE_OPEN, 0);
fd = ngx_open_file_wrapper(name, of, NGX_FILE_RDONLY|NGX_FILE_NONBLOCK,
NGX_FILE_OPEN, 0);
} else {
fd = ngx_open_file(name->data, NGX_FILE_APPEND,
NGX_FILE_CREATE_OR_OPEN,
NGX_FILE_DEFAULT_ACCESS);
fd = ngx_open_file_wrapper(name, of, NGX_FILE_APPEND,
NGX_FILE_CREATE_OR_OPEN,
NGX_FILE_DEFAULT_ACCESS);
}
if (fd == NGX_INVALID_FILE) {
of->failed = ngx_open_file_n;
goto failed;
of->fd = NGX_INVALID_FILE;
return NGX_ERROR;
}
if (ngx_fd_info(fd, &fi) == NGX_FILE_ERROR) {
@ -565,13 +790,6 @@ done:
of->is_exec = ngx_is_exec(&fi);
return NGX_OK;
failed:
of->fd = NGX_INVALID_FILE;
of->err = ngx_errno;
return NGX_ERROR;
}

8
src/core/ngx_open_file_cache.h
View File

@ -32,6 +32,10 @@ typedef struct {
ngx_uint_t min_uses;
#if (NGX_HAVE_OPENAT)
unsigned disable_symlinks:2;
#endif
unsigned test_dir:1;
unsigned test_only:1;
unsigned log:1;
@ -64,6 +68,10 @@ struct ngx_cached_open_file_s {
uint32_t uses;
#if (NGX_HAVE_OPENAT)
unsigned disable_symlinks:2;
#endif
unsigned count:24;
unsigned close:1;
unsigned use_event:1;

35
src/http/ngx_http_core_module.c
View File

@ -187,6 +187,18 @@ static ngx_str_t ngx_http_gzip_private = ngx_string("private");
#endif
#if (NGX_HAVE_OPENAT)
static ngx_conf_enum_t ngx_http_core_disable_symlinks[] = {
{ ngx_string("off"), NGX_DISABLE_SYMLINKS_OFF },
{ ngx_string("if_not_owner"), NGX_DISABLE_SYMLINKS_NOTOWNER },
{ ngx_string("on"), NGX_DISABLE_SYMLINKS_ON },
{ ngx_null_string, 0 }
};
#endif
static ngx_command_t ngx_http_core_commands[] = {
{ ngx_string("variables_hash_max_size"),
@ -762,6 +774,17 @@ static ngx_command_t ngx_http_core_commands[] = {
0,
NULL },
#endif
#if (NGX_HAVE_OPENAT)
{ ngx_string("disable_symlinks"),
NGX_HTTP_MAIN_CONF|NGX_HTTP_SRV_CONF|NGX_HTTP_LOC_CONF|NGX_CONF_TAKE1,
ngx_conf_set_enum_slot,
NGX_HTTP_LOC_CONF_OFFSET,
offsetof(ngx_http_core_loc_conf_t, disable_symlinks),
&ngx_http_core_disable_symlinks },
#endif
ngx_null_command
@ -1297,6 +1320,9 @@ ngx_http_core_try_files_phase(ngx_http_request_t *r,
of.test_only = 1;
of.errors = clcf->open_file_cache_errors;
of.events = clcf->open_file_cache_events;
#if (NGX_HAVE_OPENAT)
of.disable_symlinks = clcf->disable_symlinks;
#endif
if (ngx_open_cached_file(clcf->open_file_cache, &path, &of, r->pool)
!= NGX_OK)
@ -3344,6 +3370,10 @@ ngx_http_core_create_loc_conf(ngx_conf_t *cf)
#endif
#endif
#if (NGX_HAVE_OPENAT)
clcf->disable_symlinks = NGX_CONF_UNSET_UINT;
#endif
return clcf;
}
@ -3623,6 +3653,11 @@ ngx_http_core_merge_loc_conf(ngx_conf_t *cf, void *parent, void *child)
#endif
#endif
#if (NGX_HAVE_OPENAT)
ngx_conf_merge_uint_value(conf->disable_symlinks, prev->disable_symlinks,
NGX_DISABLE_SYMLINKS_OFF);
#endif
return NGX_CONF_OK;
}

4
src/http/ngx_http_core_module.h
View File

@ -404,6 +404,10 @@ struct ngx_http_core_loc_conf_s {
#endif
#endif
#if (NGX_HAVE_OPENAT)
ngx_uint_t disable_symlinks; /* disable_symlinks */
#endif
ngx_array_t *error_pages; /* error_page */
ngx_http_try_file_t *try_files; /* try_files */