@@ -87,6 +87,7 @@ static int fsinfo_generic_ids(struct path *path, struct fsinfo_ids *p)
p->f_fstype = sb->s_magic;
p->f_dev_major = MAJOR(sb->s_dev);
p->f_dev_minor = MINOR(sb->s_dev);
+ p->f_sb_id = sb->s_unique_id;
memcpy(&p->f_fsid, &buf.f_fsid, sizeof(p->f_fsid));
strlcpy(p->f_fs_name, path->dentry->d_sb->s_type->name,
@@ -43,6 +43,8 @@ static int thaw_super_locked(struct super_block *sb);
static LIST_HEAD(super_blocks);
static DEFINE_SPINLOCK(sb_lock);
+static u64 sb_last_identifier;
+static u64 sb_identifier_offset;
static char *sb_writers_name[SB_FREEZE_LEVELS] = {
"sb_writers",
@@ -187,6 +189,27 @@ static void destroy_unused_super(struct super_block *s)
destroy_super_work(&s->destroy_work);
}
+/*
+ * Generate a unique identifier for a superblock.
+ */
+static void generate_super_id(struct super_block *s)
+{
+ u64 id = ktime_to_ns(ktime_get());
+
+ spin_lock(&sb_lock);
+
+ id += sb_identifier_offset;
+ if (id <= sb_last_identifier) {
+ id = sb_last_identifier + 1;
+ sb_identifier_offset = sb_last_identifier - id;
+ }
+
+ sb_last_identifier = id;
+ spin_unlock(&sb_lock);
+
+ s->s_unique_id = id;
+}
+
/**
* alloc_super - create new superblock
* @type: filesystem type superblock should belong to
@@ -270,6 +293,7 @@ static struct super_block *alloc_super(struct file_system_type *type, int flags,
goto fail;
if (list_lru_init_memcg(&s->s_inode_lru, &s->s_shrink))
goto fail;
+ generate_super_id(s);
return s;
fail:
@@ -1527,6 +1527,9 @@ struct super_block {
spinlock_t s_inode_wblist_lock;
struct list_head s_inodes_wb; /* writeback inodes */
+
+ /* Superblock event notifications */
+ u64 s_unique_id;
} __randomize_layout;
/* Helper functions so that in most cases filesystems will
@@ -185,6 +185,7 @@ static void dump_attr_IDS(union reply *r, int size)
printf("\tdev : %02x:%02x\n", f->f_dev_major, f->f_dev_minor);
printf("\tfs : type=%x name=%s\n", f->f_fstype, f->f_fs_name);
printf("\tfsid : %llx\n", (unsigned long long)f->f_fsid);
+ printf("\tsbid : %llx\n", (unsigned long long)f->f_sb_id);
}
static void dump_attr_LIMITS(union reply *r, int size)
Introduce an (effectively) non-repeating system-unique superblock ID that can be used to determine that two object are in the same superblock without risking reuse of the ID in the meantime (as is possible with device IDs). The ID is time-based to make it harder to use it as a covert communications channel. Also make it so that this ID can be fetched by the fsinfo() system call. The ID added so that superblock notification messages will also be able to be tagged with it. Signed-off-by: David Howells <dhowells@redhat.com> --- fs/fsinfo.c | 1 + fs/super.c | 24 ++++++++++++++++++++++++ include/linux/fs.h | 3 +++ samples/vfs/test-fsinfo.c | 1 + 4 files changed, 29 insertions(+)