[PATCH v2] fuse: fix illegal access to inode with reused nodeid

[PATCH v2] fuse: fix illegal access to inode with reused nodeid

[Amir Goldstein]

Server responds to LOOKUP and other ops (READDIRPLUS/CREATE/MKNOD/...)
with ourarg containing nodeid and generation.

If a fuse inode is found in inode cache with the same nodeid but
different generation, the existing fuse inode should be unhashed and
marked "bad" and a new inode with the new generation should be hashed
instead.

This can happen, for example, with passhrough fuse filesystem that
returns the real filesystem ino/generation on lookup and where real inode
numbers can get recycled due to real files being unlinked not via the fuse
passthrough filesystem.

With current code, this situation will not be detected and an old fuse
dentry that used to point to an older generation real inode, can be used
to access a completely new inode, which should be accessed only via the
new dentry.

Note that because the FORGET message carries the nodeid w/o generation,
the server should wait to get FORGET counts for the nlookup counts of
the old and reused inodes combined, before it can free the resources
associated to that nodeid.

Signed-off-by: Amir Goldstein <amir73il@gmail.com>
---

Changes since v1:
- Do not include automount in fuse_stale_inode() check
- Revert unintential behavior change in fuse_dentry_revalidate()
  of wrong type inode

 fs/fuse/dir.c     | 5 +++--
 fs/fuse/fuse_i.h  | 7 +++++++
 fs/fuse/inode.c   | 4 ++--
 fs/fuse/readdir.c | 7 +++++--
 4 files changed, 17 insertions(+), 6 deletions(-)

diff --git a/fs/fuse/dir.c b/fs/fuse/dir.c
index 1b6c001a7dd1..f361bfdc8544 100644
--- a/fs/fuse/dir.c
+++ b/fs/fuse/dir.c
@@ -239,7 +239,8 @@ static int fuse_dentry_revalidate(struct dentry *entry, unsigned int flags)
 		if (!ret) {
 			fi = get_fuse_inode(inode);
 			if (outarg.nodeid != get_node_id(inode) ||
-			    (bool) IS_AUTOMOUNT(inode) != (bool) (outarg.attr.flags & FUSE_ATTR_SUBMOUNT)) {
+			    (bool) IS_AUTOMOUNT(inode) !=
+			    (bool) (outarg.attr.flags & FUSE_ATTR_SUBMOUNT)) {
 				fuse_queue_forget(fm->fc, forget,
 						  outarg.nodeid, 1);
 				goto invalid;
@@ -252,7 +253,7 @@ static int fuse_dentry_revalidate(struct dentry *entry, unsigned int flags)
 		if (ret == -ENOMEM)
 			goto out;
 		if (ret || fuse_invalid_attr(&outarg.attr) ||
-		    inode_wrong_type(inode, outarg.attr.mode))
+		    fuse_stale_inode(inode, outarg.generation, &outarg.attr))
 			goto invalid;
 
 		forget_all_cached_acls(inode);
diff --git a/fs/fuse/fuse_i.h b/fs/fuse/fuse_i.h
index 7e463e220053..d2045492ff5a 100644
--- a/fs/fuse/fuse_i.h
+++ b/fs/fuse/fuse_i.h
@@ -867,6 +867,13 @@ static inline u64 fuse_get_attr_version(struct fuse_conn *fc)
 	return atomic64_read(&fc->attr_version);
 }
 
+static inline bool fuse_stale_inode(const struct inode *inode, int generation,
+				    struct fuse_attr *attr)
+{
+	return inode->i_generation != generation ||
+		inode_wrong_type(inode, attr->mode);
+}
+
 static inline void fuse_make_bad(struct inode *inode)
 {
 	remove_inode_hash(inode);
diff --git a/fs/fuse/inode.c b/fs/fuse/inode.c
index 393e36b74dc4..257bb3e1cac8 100644
--- a/fs/fuse/inode.c
+++ b/fs/fuse/inode.c
@@ -350,8 +350,8 @@ struct inode *fuse_iget(struct super_block *sb, u64 nodeid,
 		inode->i_generation = generation;
 		fuse_init_inode(inode, attr);
 		unlock_new_inode(inode);
-	} else if (inode_wrong_type(inode, attr->mode)) {
-		/* Inode has changed type, any I/O on the old should fail */
+	} else if (fuse_stale_inode(inode, generation, attr)) {
+		/* nodeid was reused, any I/O on the old inode should fail */
 		fuse_make_bad(inode);
 		iput(inode);
 		goto retry;
diff --git a/fs/fuse/readdir.c b/fs/fuse/readdir.c
index 277f7041d55a..bc267832310c 100644
--- a/fs/fuse/readdir.c
+++ b/fs/fuse/readdir.c
@@ -200,9 +200,12 @@ static int fuse_direntplus_link(struct file *file,
 	if (!d_in_lookup(dentry)) {
 		struct fuse_inode *fi;
 		inode = d_inode(dentry);
+		if (inode && get_node_id(inode) != o->nodeid)
+			inode = NULL;
 		if (!inode ||
-		    get_node_id(inode) != o->nodeid ||
-		    inode_wrong_type(inode, o->attr.mode)) {
+		    fuse_stale_inode(inode, o->generation, &o->attr)) {
+			if (inode)
+				fuse_make_bad(inode);
 			d_invalidate(dentry);
 			dput(dentry);
 			goto retry;
-- 
2.32.0

Re: [PATCH v2] fuse: fix illegal access to inode with reused nodeid

[Miklos Szeredi]

On Mon, 21 Jun 2021 at 13:03, Amir Goldstein <amir73il@gmail.com> wrote:
>
> Server responds to LOOKUP and other ops (READDIRPLUS/CREATE/MKNOD/...)
> with ourarg containing nodeid and generation.
>
> If a fuse inode is found in inode cache with the same nodeid but
> different generation, the existing fuse inode should be unhashed and
> marked "bad" and a new inode with the new generation should be hashed
> instead.
>
> This can happen, for example, with passhrough fuse filesystem that
> returns the real filesystem ino/generation on lookup and where real inode
> numbers can get recycled due to real files being unlinked not via the fuse
> passthrough filesystem.
>
> With current code, this situation will not be detected and an old fuse
> dentry that used to point to an older generation real inode, can be used
> to access a completely new inode, which should be accessed only via the
> new dentry.
>
> Note that because the FORGET message carries the nodeid w/o generation,
> the server should wait to get FORGET counts for the nlookup counts of
> the old and reused inodes combined, before it can free the resources
> associated to that nodeid.
>
> Signed-off-by: Amir Goldstein <amir73il@gmail.com>

Applied and pushed.

Thanks,
Miklos