process-util: refactor APIs for reading /proc/self/xyz symlinks

The three functions for reading cwd, exe and root symlinks of processes
already share a common core: get_process_link_contents(). Let's refactor
that a bit, and move formatting of the /proc/self/ path into this helper
function instead of doing that in the caller, thus sharing more code.

While we are at it, make the return parameters optional, in case the
information if the links are readable is interesting, but the contents
is not. (This also means safe_getcwd() and readlinkat_malloc() are
updated to make the return parameter optional, as these are called by
the relevant three functions)

diff --git a/src/basic/fs-util.c b/src/basic/fs-util.c
index 4c81057a8974a36f0019f181cf96fe94d883d657..d67b30429c0911b9df3ddf61c909209d4f4f51cb 100644 (file)
--- a/src/basic/fs-util.c
+++ b/src/basic/fs-util.c
@@ -119,7 +119,6 @@ int readlinkat_malloc(int fd, const char *p, char **ret) {
         size_t l = PATH_MAX;
 
         assert(p);
-        assert(ret);
 
         for (;;) {
                 _cleanup_free_ char *c = NULL;
@@ -135,7 +134,10 @@ int readlinkat_malloc(int fd, const char *p, char **ret) {
 
                 if ((size_t) n < l) {
                         c[n] = 0;
-                        *ret = TAKE_PTR(c);
+
+                        if (ret)
+                                *ret = TAKE_PTR(c);
+
                         return 0;
                 }
 

diff --git a/src/basic/path-util.c b/src/basic/path-util.c
index 0be2b9eec813e7160edc352fc917c06438f17103..92ee3cee2d12a2f8abbafeba9373d76682e03725 100644 (file)
--- a/src/basic/path-util.c
+++ b/src/basic/path-util.c
@@ -63,7 +63,7 @@ char *path_make_absolute(const char *p, const char *prefix) {
 }
 
 int safe_getcwd(char **ret) {
-        char *cwd;
+        _cleanup_free_ char *cwd = NULL;
 
         cwd = get_current_dir_name();
         if (!cwd)
@@ -71,12 +71,12 @@ int safe_getcwd(char **ret) {
 
         /* Let's make sure the directory is really absolute, to protect us from the logic behind
          * CVE-2018-1000001 */
-        if (cwd[0] != '/') {
-                free(cwd);
+        if (cwd[0] != '/')
                 return -ENOMEDIUM;
-        }
 
-        *ret = cwd;
+        if (ret)
+                *ret = TAKE_PTR(cwd);
+
         return 0;
 }
 

diff --git a/src/basic/process-util.c b/src/basic/process-util.c
index 10aec10bfa721faa26e1fc1a363de434e32ffe75..204a5d949011aa9eec5c635803d4d7ebb2de199d 100644 (file)
--- a/src/basic/process-util.c
+++ b/src/basic/process-util.c
@@ -472,37 +472,33 @@ int get_process_capeff(pid_t pid, char **ret) {
         return r;
 }
 
-static int get_process_link_contents(const char *proc_file, char **ret) {
+static int get_process_link_contents(pid_t pid, const char *proc_file, char **ret) {
+        const char *p;
         int r;
 
         assert(proc_file);
-        assert(ret);
 
-        r = readlink_malloc(proc_file, ret);
-        if (r == -ENOENT)
-                return -ESRCH;
-        if (r < 0)
-                return r;
+        p = procfs_file_alloca(pid, proc_file);
 
-        return 0;
+        r = readlink_malloc(p, ret);
+        return r == -ENOENT ? -ESRCH : r;
 }
 
 int get_process_exe(pid_t pid, char **ret) {
-        const char *p;
         char *d;
         int r;
 
         assert(pid >= 0);
-        assert(ret);
 
-        p = procfs_file_alloca(pid, "exe");
-        r = get_process_link_contents(p, ret);
+        r = get_process_link_contents(pid, "exe", ret);
         if (r < 0)
                 return r;
 
-        d = endswith(*ret, " (deleted)");
-        if (d)
-                *d = '\0';
+        if (ret) {
+                d = endswith(*ret, " (deleted)");
+                if (d)
+                        *d = '\0';
+        }
 
         return 0;
 }
@@ -572,28 +568,17 @@ int get_process_gid(pid_t pid, gid_t *ret) {
 }
 
 int get_process_cwd(pid_t pid, char **ret) {
-        const char *p;
-
         assert(pid >= 0);
-        assert(ret);
 
         if (pid == 0 || pid == getpid_cached())
                 return safe_getcwd(ret);
 
-        p = procfs_file_alloca(pid, "cwd");
-
-        return get_process_link_contents(p, ret);
+        return get_process_link_contents(pid, "cwd", ret);
 }
 
 int get_process_root(pid_t pid, char **ret) {
-        const char *p;
-
         assert(pid >= 0);
-        assert(ret);
-
-        p = procfs_file_alloca(pid, "root");
-
-        return get_process_link_contents(p, ret);
+        return get_process_link_contents(pid, "root", ret);
 }
 
 #define ENVIRONMENT_BLOCK_MAX (5U*1024U*1024U)