From 9948b4668c992611de2be5c58845a7070e5af032 Mon Sep 17 00:00:00 2001
From: Lennart Poettering <lennart@poettering.net>
Date: Wed, 27 Nov 2024 14:54:36 +0100
Subject: [PATCH] virt: drop userns detection heuristic

Now that we have an explicit userns check we can drop the heuristic for
it, given that it's kinda wrong (because mapping the full host UID range
into a userns is actually a thing people do).

Hence, just delete the code and only keep the userns inode check in
place.
---
 src/basic/virt.c | 63 ++----------------------------------------------
 1 file changed, 2 insertions(+), 61 deletions(-)

diff --git a/src/basic/virt.c b/src/basic/virt.c
index 7f9a7e9a249..88a406ef227 100644
--- a/src/basic/virt.c
+++ b/src/basic/virt.c
@@ -20,7 +20,6 @@
 #include "stat-util.h"
 #include "string-table.h"
 #include "string-util.h"
-#include "uid-range.h"
 #include "virt.h"
 
 enum {
@@ -772,72 +771,14 @@ Virtualization detect_virtualization(void) {
         return detect_vm();
 }
 
-static int userns_has_mapping(const char *name) {
-        _cleanup_fclose_ FILE *f = NULL;
-        uid_t base, shift, range;
-        int r;
-
-        f = fopen(name, "re");
-        if (!f) {
-                log_debug_errno(errno, "Failed to open %s: %m", name);
-                return errno == ENOENT ? false : -errno;
-        }
-
-        r = uid_map_read_one(f, &base, &shift, &range);
-        if (r == -ENOMSG) {
-                log_debug("%s is empty, we're in an uninitialized user namespace.", name);
-                return true;
-        }
-        if (r < 0)
-                return log_debug_errno(r, "Failed to read %s: %m", name);
-
-        if (base == 0 && shift == 0 && range == UINT32_MAX) {
-                /* The kernel calls mappings_overlap() and does not allow overlaps */
-                log_debug("%s has a full 1:1 mapping", name);
-                return false;
-        }
-
-        /* Anything else implies that we are in a user namespace */
-        log_debug("Mapping found in %s, we're in a user namespace.", name);
-        return true;
-}
-
 int running_in_userns(void) {
-        _cleanup_free_ char *line = NULL;
         int r;
 
         r = namespace_is_init(NAMESPACE_USER);
         if (r < 0)
-                log_debug_errno(r, "Failed to test if in root user namespace, ignoring: %m");
-        else if (r > 0)
-                return false;
-
-        // FIXME: We really should drop the heuristics below.
-
-        r = userns_has_mapping("/proc/self/uid_map");
-        if (r != 0)
-                return r;
-
-        r = userns_has_mapping("/proc/self/gid_map");
-        if (r != 0)
-                return r;
+                return log_debug_errno(r, "Failed to test if in root user namespace, ignoring: %m");
 
-        /* "setgroups" file was added in kernel v3.18-rc6-15-g9cc46516dd. It is also possible to compile a
-         * kernel without CONFIG_USER_NS, in which case "setgroups" also does not exist. We cannot
-         * distinguish those two cases, so assume that we're running on a stripped-down recent kernel, rather
-         * than on an old one, and if the file is not found, return false. */
-        r = read_virtual_file("/proc/self/setgroups", SIZE_MAX, &line, NULL);
-        if (r < 0) {
-                log_debug_errno(r, "/proc/self/setgroups: %m");
-                return r == -ENOENT ? false : r;
-        }
-
-        strstrip(line); /* remove trailing newline */
-
-        r = streq(line, "deny");
-        /* See user_namespaces(7) for a description of this "setgroups" contents. */
-        log_debug("/proc/self/setgroups contains \"%s\", %s user namespace", line, r ? "in" : "not in");
-        return r;
+        return !r;
 }
 
 int running_in_chroot(void) {
-- 
2.47.3