Merge pull request #15564 from poettering/tmpfiles-no-proc

util-lib: check for /proc being mounted in some really basic fs operations

src/basic/fd-util.c

@@ -21,9 +21,10 @@
 #include "path-util.h"
 #include "process-util.h"
 #include "socket-util.h"
+#include "stat-util.h"
 #include "stdio-util.h"
-#include "util.h"
 #include "tmpfile-util.h"
+#include "util.h"
 
 /* The maximum number of iterations in the loop to close descriptors in the fallback case
  * when /proc/self/fd/ is inaccessible. */
@@ -939,8 +940,15 @@ int fd_reopen(int fd, int flags) {
 
         xsprintf(procfs_path, "/proc/self/fd/%i", fd);
         new_fd = open(procfs_path, flags);
-        if (new_fd < 0)
-                return -errno;
+        if (new_fd < 0) {
+                if (errno != ENOENT)
+                        return -errno;
+
+                if (proc_mounted() == 0)
+                        return -ENOSYS; /* if we have no /proc/, the concept is not implementable */
+
+                return -ENOENT;
+        }
 
         return new_fd;
 }

src/basic/fs-util.c

@@ -337,8 +337,15 @@ int fchmod_opath(int fd, mode_t m) {
          * fchownat() does. */
 
         xsprintf(procfs_path, "/proc/self/fd/%i", fd);
-        if (chmod(procfs_path, m) < 0)
-                return -errno;
+        if (chmod(procfs_path, m) < 0) {
+                if (errno != ENOENT)
+                        return -errno;
+
+                if (proc_mounted() == 0)
+                        return -ENOSYS; /* if we have no /proc/, the concept is not implementable */
+
+                return -ENOENT;
+        }
 
         return 0;
 }

src/basic/stat-util.c

@@ -178,13 +178,12 @@ int fd_is_fs_type(int fd, statfs_f_type_t magic_value) {
 }
 
 int path_is_fs_type(const char *path, statfs_f_type_t magic_value) {
-        _cleanup_close_ int fd = -1;
+        struct statfs s;
 
-        fd = open(path, O_RDONLY|O_CLOEXEC|O_NOCTTY|O_PATH);
-        if (fd < 0)
+        if (statfs(path, &s) < 0)
                 return -errno;
 
-        return fd_is_fs_type(fd, magic_value);
+        return is_fs_type(&s, magic_value);
 }
 
 bool is_temporary_fs(const struct statfs *s) {
@@ -377,3 +376,15 @@ int device_path_parse_major_minor(const char *path, mode_t *ret_mode, dev_t *ret
 
         return 0;
 }
+
+int proc_mounted(void) {
+        int r;
+
+        /* A quick check of procfs is properly mounted */
+
+        r = path_is_fs_type("/proc/", PROC_SUPER_MAGIC);
+        if (r == -ENOENT) /* not mounted at all */
+                return false;
+
+        return r;
+}

src/basic/stat-util.h

@@ -87,3 +87,5 @@ int fd_verify_directory(int fd);
 int device_path_make_major_minor(mode_t mode, dev_t devno, char **ret);
 int device_path_make_canonical(mode_t mode, dev_t devno, char **ret);
 int device_path_parse_major_minor(const char *path, mode_t *ret_mode, dev_t *ret_devno);
+
+int proc_mounted(void);