base-filesystem: avoid creating /lib64 symlink on existing rootfs

Forwarded: yes
Bug-Debian: https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=1079329

Gbp-Pq: Name 0001-base-filesystem-avoid-creating-lib64-symlink-on-exis.patch

diff --git a/src/shared/base-filesystem.c b/src/shared/base-filesystem.c
index 389c77eee0ea3fe42955edf448ed65181f4ab753..200fe6887513ecc81e3b278ee07f2040b1e6972a 100644 (file)
--- a/src/shared/base-filesystem.c
+++ b/src/shared/base-filesystem.c
@@ -21,26 +21,32 @@
 #include "umask-util.h"
 #include "user-util.h"
 
+typedef enum BaseFilesystemFlags {
+        BASE_FILESYSTEM_IGNORE_ON_FAILURE = 1 << 0,
+        BASE_FILESYSTEM_EMPTY_MARKER      = 1 << 1, /* If this is missing, then we are booting on an empty filesystem - see comment below */
+        BASE_FILESYSTEM_EMPTY_ONLY        = 1 << 2, /* If booting on an empty filesystem create this, otherwise skip it - see comment below */
+} BaseFilesystemFlags;
+
 typedef struct BaseFilesystem {
         const char *dir;      /* directory or symlink to create */
         mode_t mode;
         const char *target;   /* if non-NULL create as symlink to this target */
         const char *exists;   /* conditionalize this entry on existence of this file */
-        bool ignore_failure;
+        BaseFilesystemFlags flags; /* various modifiers for behaviour on creation */
 } BaseFilesystem;
 
 static const BaseFilesystem table[] = {
-        { "bin",      0, "usr/bin\0",                  NULL },
-        { "lib",      0, "usr/lib\0",                  NULL },
-        { "root",  0750, NULL,                         NULL, true },
-        { "sbin",     0, "usr/sbin\0",                 NULL },
+        { "bin",      0, "usr/bin\0",                  NULL,                        BASE_FILESYSTEM_EMPTY_MARKER      },
+        { "lib",      0, "usr/lib\0",                  NULL,                        BASE_FILESYSTEM_EMPTY_MARKER      },
+        { "root",  0750, NULL,                         NULL,                        BASE_FILESYSTEM_IGNORE_ON_FAILURE },
+        { "sbin",     0, "usr/sbin\0",                 NULL,                        BASE_FILESYSTEM_EMPTY_MARKER      },
         { "usr",   0755, NULL,                         NULL },
         { "var",   0755, NULL,                         NULL },
         { "etc",   0755, NULL,                         NULL },
-        { "proc",  0555, NULL,                         NULL, true },
-        { "sys",   0555, NULL,                         NULL, true },
-        { "dev",   0555, NULL,                         NULL, true },
-        { "run",   0555, NULL,                         NULL, true },
+        { "proc",  0555, NULL,                         NULL,                        BASE_FILESYSTEM_IGNORE_ON_FAILURE },
+        { "sys",   0555, NULL,                         NULL,                        BASE_FILESYSTEM_IGNORE_ON_FAILURE },
+        { "dev",   0555, NULL,                         NULL,                        BASE_FILESYSTEM_IGNORE_ON_FAILURE },
+        { "run",   0555, NULL,                         NULL,                        BASE_FILESYSTEM_IGNORE_ON_FAILURE },
         /* We don't add /tmp/ here for now (even though it's necessary for regular operation), because we
          * want to support both cases where /tmp/ is a mount of its own (in which case we probably should set
          * the mode to 1555, to indicate that no one should write to it, not even root) and when it's part of
@@ -55,9 +61,15 @@ static const BaseFilesystem table[] = {
 #if defined(__aarch64__)
         /* aarch64 ELF ABI actually says dynamic loader is in /lib/, but Fedora puts it in /lib64/ anyway and
          * just symlinks /lib/ld-linux-aarch64.so.1 to ../lib64/ld-linux-aarch64.so.1. For this to work
-         * correctly, /lib64/ must be symlinked to /usr/lib64/. */
+         * correctly, /lib64/ must be symlinked to /usr/lib64/. On the flip side, we must not create /lib64/
+         * on Debian and derivatives as they expect the target to be different from what Fedora et al. use,
+         * which is problematic for example when nspawn from some other distribution boots a Debian
+         * container with only /usr/, so we only create this symlink when at least one other symlink is
+         * missing, and let the image builder/package manager worry about not creating incomplete persistent
+         * filesystem hierarchies instead. The key purpose of this code is to ensure we can bring up a system
+         * with a volatile root filesystem after all. */
         { "lib64",    0, "usr/lib64\0"
-                         "usr/lib\0",                "ld-linux-aarch64.so.1" },
+                         "usr/lib\0",                "ld-linux-aarch64.so.1",       BASE_FILESYSTEM_EMPTY_ONLY        },
 #  define KNOW_LIB64_DIRS 1
 #elif defined(__alpha__)
 #elif defined(__arc__) || defined(__tilegx__)
@@ -108,14 +120,15 @@ static const BaseFilesystem table[] = {
 #  elif __riscv_xlen == 64
         /* Same situation as for aarch64 */
         { "lib64",    0, "usr/lib64\0"
-                         "usr/lib\0",                "ld-linux-riscv64-lp64d.so.1" },
+                         "usr/lib\0",                "ld-linux-riscv64-lp64d.so.1", BASE_FILESYSTEM_EMPTY_ONLY        },
 #    define KNOW_LIB64_DIRS 1
 #  else
 #    error "Unknown RISC-V ABI"
 #  endif
 #elif defined(__s390x__)
+        /* Same situation as for aarch64 */
         { "lib64",    0, "usr/lib64\0"
-                         "usr/lib\0",                "ld-lsb-s390x.so.3" },
+                         "usr/lib\0",                "ld-lsb-s390x.so.3",           BASE_FILESYSTEM_EMPTY_ONLY        },
 #    define KNOW_LIB64_DIRS 1
 #elif defined(__s390__)
         /* s390-linux-gnu */
@@ -129,6 +142,7 @@ static const BaseFilesystem table[] = {
 #endif
 
 int base_filesystem_create_fd(int fd, const char *root, uid_t uid, gid_t gid) {
+        bool empty_fs = false;
         int r;
 
         assert(fd >= 0);
@@ -137,9 +151,15 @@ int base_filesystem_create_fd(int fd, const char *root, uid_t uid, gid_t gid) {
         /* The "root" parameter is decoration only – it's only used as part of log messages */
 
         FOREACH_ELEMENT(i, table) {
+                if (FLAGS_SET(i->flags, BASE_FILESYSTEM_EMPTY_ONLY) && !empty_fs)
+                        continue;
+
                 if (faccessat(fd, i->dir, F_OK, AT_SYMLINK_NOFOLLOW) >= 0)
                         continue;
 
+                if (FLAGS_SET(i->flags, BASE_FILESYSTEM_EMPTY_MARKER))
+                        empty_fs = true;
+
                 if (i->target) { /* Create as symlink? */
                         const char *target = NULL;
 
@@ -174,7 +194,7 @@ int base_filesystem_create_fd(int fd, const char *root, uid_t uid, gid_t gid) {
                                 r = RET_NERRNO(mkdirat(fd, i->dir, i->mode));
                 }
                 if (r < 0) {
-                        bool ignore = IN_SET(r, -EEXIST, -EROFS) || i->ignore_failure;
+                        bool ignore = IN_SET(r, -EEXIST, -EROFS) || FLAGS_SET(i->flags, BASE_FILESYSTEM_IGNORE_ON_FAILURE);
                         log_full_errno(ignore ? LOG_DEBUG : LOG_ERR, r,
                                        "Failed to create %s/%s: %m", root, i->dir);
                         if (ignore)