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Registered in England and Wales under Company Registration No. 3798903 Subject: [PATCH 06/25] vfs: Introduce a non-repeating system-unique superblock ID [ver #13] From: David Howells To: viro@zeniv.linux.org.uk Cc: dhowells@redhat.com, raven@themaw.net, linux-api@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, mszeredi@redhat.com Date: Tue, 28 May 2019 16:11:52 +0100 Message-ID: <155905631215.1662.17611579248841782314.stgit@warthog.procyon.org.uk> In-Reply-To: <155905626142.1662.18430571708534506785.stgit@warthog.procyon.org.uk> References: <155905626142.1662.18430571708534506785.stgit@warthog.procyon.org.uk> User-Agent: StGit/unknown-version MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7bit X-Scanned-By: MIMEDefang 2.79 on 10.5.11.12 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.38]); Tue, 28 May 2019 15:11:55 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Introduce a non-repeating system-unique superblock ID that can be used to tag superblock notification messages. The ID is time-based to make it harder to use it as a covert communications channel. Make it so that this ID can be fetched by the fsinfo() system call. Signed-off-by: David Howells --- fs/fsinfo.c | 1 + fs/super.c | 24 ++++++++++++++++++++++++ include/linux/fs.h | 3 +++ samples/vfs/test-fsinfo.c | 1 + 4 files changed, 29 insertions(+) diff --git a/fs/fsinfo.c b/fs/fsinfo.c index 256a87b62eed..6afeabfe9451 100644 --- a/fs/fsinfo.c +++ b/fs/fsinfo.c @@ -92,6 +92,7 @@ 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, diff --git a/fs/super.c b/fs/super.c index 27b3e41394c8..61819e8e5469 100644 --- a/fs/super.c +++ b/fs/super.c @@ -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: diff --git a/include/linux/fs.h b/include/linux/fs.h index 71ce3b054c42..f1c74596cd77 100644 --- a/include/linux/fs.h +++ b/include/linux/fs.h @@ -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 diff --git a/samples/vfs/test-fsinfo.c b/samples/vfs/test-fsinfo.c index e98384e8fb46..90926024e1c5 100644 --- a/samples/vfs/test-fsinfo.c +++ b/samples/vfs/test-fsinfo.c @@ -179,6 +179,7 @@ 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)