pid1: stop limiting size of /dev/shm

The explicit limit is dropped, which means that we return to the kernel default
of 50% of RAM. See 362a55fc14 for a discussion why that is not as much as it
seems. It turns out various applications need more space in /dev/shm and we
would break them by imposing a low limit.

While at it, rename the define and use a single macro for various tmpfs mounts.
We don't really care what the purpose of the given tmpfs is, so it seems
reasonable to use a single macro.

This effectively reverts part of 7d85383edbab7. Fixes #16617.

4 files changed, 28 insertions, 32 deletions

diff --git a/src/core/mount-setup.c b/src/core/mount-setup.c
index 028c4de280..feb88f3e6e 100644
--- a/src/core/mount-setup.c
+++ b/src/core/mount-setup.c
@@ -61,51 +61,51 @@ typedef struct MountPoint {
 #endif
 
 static const MountPoint mount_table[] = {
-        { "sysfs",       "/sys",                      "sysfs",      NULL,                                           MS_NOSUID|MS_NOEXEC|MS_NODEV,
+        { "sysfs",       "/sys",                      "sysfs",      NULL,                                      MS_NOSUID|MS_NOEXEC|MS_NODEV,
           NULL,          MNT_FATAL|MNT_IN_CONTAINER },
-        { "proc",        "/proc",                     "proc",       NULL,                                           MS_NOSUID|MS_NOEXEC|MS_NODEV,
+        { "proc",        "/proc",                     "proc",       NULL,                                      MS_NOSUID|MS_NOEXEC|MS_NODEV,
           NULL,          MNT_FATAL|MNT_IN_CONTAINER },
-        { "devtmpfs",    "/dev",                      "devtmpfs",   "mode=755" TMPFS_LIMITS_DEV,                    MS_NOSUID|MS_NOEXEC|MS_STRICTATIME,
+        { "devtmpfs",    "/dev",                      "devtmpfs",   "mode=755" TMPFS_LIMITS_DEV,               MS_NOSUID|MS_NOEXEC|MS_STRICTATIME,
           NULL,          MNT_FATAL|MNT_IN_CONTAINER },
-        { "securityfs",  "/sys/kernel/security",      "securityfs", NULL,                                           MS_NOSUID|MS_NOEXEC|MS_NODEV,
+        { "securityfs",  "/sys/kernel/security",      "securityfs", NULL,                                      MS_NOSUID|MS_NOEXEC|MS_NODEV,
           NULL,          MNT_NONE                   },
 #if ENABLE_SMACK
-        { "smackfs",     "/sys/fs/smackfs",           "smackfs",    "smackfsdef=*",                                 MS_NOSUID|MS_NOEXEC|MS_NODEV,
+        { "smackfs",     "/sys/fs/smackfs",           "smackfs",    "smackfsdef=*",                            MS_NOSUID|MS_NOEXEC|MS_NODEV,
           mac_smack_use, MNT_FATAL                  },
-        { "tmpfs",       "/dev/shm",                  "tmpfs",      "mode=1777,smackfsroot=*" TMPFS_LIMITS_DEV_SHM, MS_NOSUID|MS_NODEV|MS_STRICTATIME,
+        { "tmpfs",       "/dev/shm",                  "tmpfs",      "mode=1777,smackfsroot=*",                 MS_NOSUID|MS_NODEV|MS_STRICTATIME,
           mac_smack_use, MNT_FATAL                  },
 #endif
-        { "tmpfs",       "/dev/shm",                  "tmpfs",      "mode=1777" TMPFS_LIMITS_DEV_SHM,               MS_NOSUID|MS_NODEV|MS_STRICTATIME,
+        { "tmpfs",       "/dev/shm",                  "tmpfs",      "mode=1777",                               MS_NOSUID|MS_NODEV|MS_STRICTATIME,
           NULL,          MNT_FATAL|MNT_IN_CONTAINER },
-        { "devpts",      "/dev/pts",                  "devpts",     "mode=620,gid=" STRINGIFY(TTY_GID),             MS_NOSUID|MS_NOEXEC,
+        { "devpts",      "/dev/pts",                  "devpts",     "mode=620,gid=" STRINGIFY(TTY_GID),        MS_NOSUID|MS_NOEXEC,
           NULL,          MNT_IN_CONTAINER           },
 #if ENABLE_SMACK
-        { "tmpfs",       "/run",                      "tmpfs",      "mode=755,smackfsroot=*" TMPFS_LIMITS_RUN,      MS_NOSUID|MS_NODEV|MS_STRICTATIME,
+        { "tmpfs",       "/run",                      "tmpfs",      "mode=755,smackfsroot=*" TMPFS_LIMITS_RUN, MS_NOSUID|MS_NODEV|MS_STRICTATIME,
           mac_smack_use, MNT_FATAL                  },
 #endif
-        { "tmpfs",       "/run",                      "tmpfs",      "mode=755" TMPFS_LIMITS_RUN,                    MS_NOSUID|MS_NODEV|MS_STRICTATIME,
+        { "tmpfs",       "/run",                      "tmpfs",      "mode=755" TMPFS_LIMITS_RUN,               MS_NOSUID|MS_NODEV|MS_STRICTATIME,
           NULL,          MNT_FATAL|MNT_IN_CONTAINER },
-        { "cgroup2",     "/sys/fs/cgroup",            "cgroup2",    "nsdelegate",                                   MS_NOSUID|MS_NOEXEC|MS_NODEV,
+        { "cgroup2",     "/sys/fs/cgroup",            "cgroup2",    "nsdelegate",                              MS_NOSUID|MS_NOEXEC|MS_NODEV,
           cg_is_unified_wanted, MNT_IN_CONTAINER|MNT_CHECK_WRITABLE },
-        { "cgroup2",     "/sys/fs/cgroup",            "cgroup2",    NULL,                                           MS_NOSUID|MS_NOEXEC|MS_NODEV,
+        { "cgroup2",     "/sys/fs/cgroup",            "cgroup2",    NULL,                                      MS_NOSUID|MS_NOEXEC|MS_NODEV,
           cg_is_unified_wanted, MNT_IN_CONTAINER|MNT_CHECK_WRITABLE },
-        { "tmpfs",       "/sys/fs/cgroup",            "tmpfs",      "mode=755" TMPFS_LIMITS_SYS_FS_CGROUP,          MS_NOSUID|MS_NOEXEC|MS_NODEV|MS_STRICTATIME,
+        { "tmpfs",       "/sys/fs/cgroup",            "tmpfs",      "mode=755" TMPFS_LIMITS_SYS_FS_CGROUP,     MS_NOSUID|MS_NOEXEC|MS_NODEV|MS_STRICTATIME,
           cg_is_legacy_wanted, MNT_FATAL|MNT_IN_CONTAINER },
-        { "cgroup2",     "/sys/fs/cgroup/unified",    "cgroup2",    "nsdelegate",                                   MS_NOSUID|MS_NOEXEC|MS_NODEV,
+        { "cgroup2",     "/sys/fs/cgroup/unified",    "cgroup2",    "nsdelegate",                              MS_NOSUID|MS_NOEXEC|MS_NODEV,
           cg_is_hybrid_wanted, MNT_IN_CONTAINER|MNT_CHECK_WRITABLE },
-        { "cgroup2",     "/sys/fs/cgroup/unified",    "cgroup2",    NULL,                                           MS_NOSUID|MS_NOEXEC|MS_NODEV,
+        { "cgroup2",     "/sys/fs/cgroup/unified",    "cgroup2",    NULL,                                      MS_NOSUID|MS_NOEXEC|MS_NODEV,
           cg_is_hybrid_wanted, MNT_IN_CONTAINER|MNT_CHECK_WRITABLE },
-        { "cgroup",      "/sys/fs/cgroup/systemd",    "cgroup",     "none,name=systemd,xattr",                      MS_NOSUID|MS_NOEXEC|MS_NODEV,
+        { "cgroup",      "/sys/fs/cgroup/systemd",    "cgroup",     "none,name=systemd,xattr",                 MS_NOSUID|MS_NOEXEC|MS_NODEV,
           cg_is_legacy_wanted, MNT_IN_CONTAINER     },
-        { "cgroup",      "/sys/fs/cgroup/systemd",    "cgroup",     "none,name=systemd",                            MS_NOSUID|MS_NOEXEC|MS_NODEV,
+        { "cgroup",      "/sys/fs/cgroup/systemd",    "cgroup",     "none,name=systemd",                       MS_NOSUID|MS_NOEXEC|MS_NODEV,
           cg_is_legacy_wanted, MNT_FATAL|MNT_IN_CONTAINER },
-        { "pstore",      "/sys/fs/pstore",            "pstore",     NULL,                                           MS_NOSUID|MS_NOEXEC|MS_NODEV,
+        { "pstore",      "/sys/fs/pstore",            "pstore",     NULL,                                      MS_NOSUID|MS_NOEXEC|MS_NODEV,
           NULL,          MNT_NONE                   },
 #if ENABLE_EFI
-        { "efivarfs",    "/sys/firmware/efi/efivars", "efivarfs",   NULL,                                           MS_NOSUID|MS_NOEXEC|MS_NODEV,
+        { "efivarfs",    "/sys/firmware/efi/efivars", "efivarfs",   NULL,                                      MS_NOSUID|MS_NOEXEC|MS_NODEV,
           is_efi_boot,   MNT_NONE                   },
 #endif
-        { "bpf",         "/sys/fs/bpf",               "bpf",        "mode=700",                                     MS_NOSUID|MS_NOEXEC|MS_NODEV,
+        { "bpf",         "/sys/fs/bpf",               "bpf",        "mode=700",                                MS_NOSUID|MS_NOEXEC|MS_NODEV,
           NULL,          MNT_NONE,                  },
 };
 
diff --git a/src/core/namespace.c b/src/core/namespace.c
index 5865dfe93e..36d5ff67ae 100644
--- a/src/core/namespace.c
+++ b/src/core/namespace.c
@@ -326,23 +326,21 @@ static int append_bind_mounts(MountEntry **p, const BindMount *binds, size_t n)
 }
 
 static int append_tmpfs_mounts(MountEntry **p, const TemporaryFileSystem *tmpfs, size_t n) {
-        size_t i;
-        int r;
-
         assert(p);
 
-        for (i = 0; i < n; i++) {
+        for (size_t i = 0; i < n; i++) {
                 const TemporaryFileSystem *t = tmpfs + i;
                 _cleanup_free_ char *o = NULL, *str = NULL;
                 unsigned long flags;
                 bool ro = false;
+                int r;
 
                 if (!path_is_absolute(t->path))
                         return log_debug_errno(SYNTHETIC_ERRNO(EINVAL),
                                                "Path is not absolute: %s",
                                                t->path);
 
-                str = strjoin("mode=0755" TMPFS_LIMITS_TEMPORARY_FS ",", t->options);
+                str = strjoin("mode=0755" NESTED_TMPFS_LIMITS ",", t->options);
                 if (!str)
                         return -ENOMEM;
 
diff --git a/src/nspawn/nspawn-mount.c b/src/nspawn/nspawn-mount.c
index a48c7f62da..5599c6a1b3 100644
--- a/src/nspawn/nspawn-mount.c
+++ b/src/nspawn/nspawn-mount.c
@@ -549,7 +549,7 @@ int mount_all(const char *dest,
                   MOUNT_IN_USERNS|MOUNT_MKDIR },
 
                 /* Then we list outer child mounts (i.e. mounts applied *before* entering user namespacing) */
-                { "tmpfs",                  "/tmp",                         "tmpfs", "mode=1777" TMPFS_LIMITS_TMP,     MS_NOSUID|MS_NODEV|MS_STRICTATIME,
+                { "tmpfs",                  "/tmp",                         "tmpfs", "mode=1777" NESTED_TMPFS_LIMITS,  MS_NOSUID|MS_NODEV|MS_STRICTATIME,
                   MOUNT_FATAL|MOUNT_APPLY_TMPFS_TMP|MOUNT_MKDIR },
                 { "tmpfs",                  "/sys",                         "tmpfs", "mode=555" TMPFS_LIMITS_SYS,      MS_NOSUID|MS_NOEXEC|MS_NODEV,
                   MOUNT_FATAL|MOUNT_APPLY_APIVFS_NETNS|MOUNT_MKDIR },
@@ -559,7 +559,7 @@ int mount_all(const char *dest,
                   MOUNT_FATAL|MOUNT_MKDIR },                          /* skipped if above was mounted */
                 { "tmpfs",                  "/dev",                         "tmpfs", "mode=755" TMPFS_LIMITS_DEV,      MS_NOSUID|MS_STRICTATIME,
                   MOUNT_FATAL|MOUNT_MKDIR },
-                { "tmpfs",                  "/dev/shm",                     "tmpfs", "mode=1777" TMPFS_LIMITS_DEV_SHM, MS_NOSUID|MS_NODEV|MS_STRICTATIME,
+                { "tmpfs",                  "/dev/shm",                     "tmpfs", "mode=1777" NESTED_TMPFS_LIMITS,  MS_NOSUID|MS_NODEV|MS_STRICTATIME,
                   MOUNT_FATAL|MOUNT_MKDIR },
                 { "tmpfs",                  "/run",                         "tmpfs", "mode=755" TMPFS_LIMITS_RUN,      MS_NOSUID|MS_NODEV|MS_STRICTATIME,
                   MOUNT_FATAL|MOUNT_MKDIR },
diff --git a/src/shared/mount-util.h b/src/shared/mount-util.h
index 7bad3743e0..8fb597e7c0 100644
--- a/src/shared/mount-util.h
+++ b/src/shared/mount-util.h
@@ -21,13 +21,11 @@
  * PID1 because 16MB of free space is required. */
 #define TMPFS_LIMITS_RUN             ",size=20%,nr_inodes=800k"
 
-/* The limit used for various tmpfs mounts, but not /tmp itself.
+/* The limit used for various nested tmpfs mounts, in paricular for guests started by systemd-nspawn.
  * 10% of RAM (using 16GB of RAM as a baseline) translates to 400k inodes (assuming 4k each) and 25%
  * translates to 1M inodes.
- * /tmp is configured through a .mount unit file. */
-#define TMPFS_LIMITS_TMP             ",size=10%,nr_inodes=400k"
-#define TMPFS_LIMITS_DEV_SHM         TMPFS_LIMITS_TMP
-#define TMPFS_LIMITS_TEMPORARY_FS    TMPFS_LIMITS_TMP
+ * (On the host, /tmp is configured through a .mount unit file.) */
+#define NESTED_TMPFS_LIMITS          ",size=10%,nr_inodes=400k"
 
 /* More space for volatile root and /var */
 #define TMPFS_LIMITS_VAR             ",size=25%,nr_inodes=1m"