util-lib: rework /tmp and /var/tmp handling code

Beef up the existing var_tmp() call, rename it to var_tmp_dir() and add a
matching tmp_dir() call (the former looks for the place for /var/tmp, the
latter for /tmp).

Both calls check $TMPDIR, $TEMP, $TMP, following the algorithm Python3 uses.
All dirs are validated before use. secure_getenv() is used in order to limite
exposure in suid binaries.

This also ports a couple of users over to these new APIs.

The var_tmp() return parameter is changed from an allocated buffer the caller
will own to a const string either pointing into environ[], or into a static
const buffer. Given that environ[] is mostly considered constant (and this is
exposed in the very well-known getenv() call), this should be OK behaviour and
allows us to avoid memory allocations in most cases.

Note that $TMPDIR and friends override both /var/tmp and /tmp usage if set.

1 files changed, 8 insertions, 1 deletions

diff --git a/src/coredump/coredumpctl.c b/src/coredump/coredumpctl.c
index 27b1e0fb3f..bbf8793e57 100644
--- a/src/coredump/coredumpctl.c
+++ b/src/coredump/coredumpctl.c
@@ -30,6 +30,7 @@
 #include "compress.h"
 #include "fd-util.h"
 #include "fileio.h"
+#include "fs-util.h"
 #include "journal-internal.h"
 #include "log.h"
 #include "macro.h"
@@ -609,7 +610,13 @@ static int save_core(sd_journal *j, int fd, char **path, bool *unlink_temp) {
                 char *temp = NULL;
 
                 if (fd < 0) {
-                        temp = strdup("/var/tmp/coredump-XXXXXX");
+                        const char *vt;
+
+                        r = var_tmp_dir(&vt);
+                        if (r < 0)
+                                return log_error_errno(r, "Failed to acquire temporary directory path: %m");
+
+                        temp = strjoin(vt, "/coredump-XXXXXX", NULL);
                         if (!temp)
                                 return log_oom();