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    Subject[PATCH 5.13 171/351] fuse: fix illegal access to inode with reused nodeid
    Date
    From: Amir Goldstein <amir73il@gmail.com>

    [ Upstream commit 15db16837a35d8007cb8563358787412213db25e ]

    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>
    Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
    Signed-off-by: Sasha Levin <sashal@kernel.org>
    ---
    fs/fuse/dir.c | 2 +-
    fs/fuse/fuse_i.h | 7 +++++++
    fs/fuse/inode.c | 4 ++--
    fs/fuse/readdir.c | 7 +++++--
    4 files changed, 15 insertions(+), 5 deletions(-)

    diff --git a/fs/fuse/dir.c b/fs/fuse/dir.c
    index 3fa8604c21d5..d296b0d19c27 100644
    --- a/fs/fuse/dir.c
    +++ b/fs/fuse/dir.c
    @@ -252,7 +252,7 @@ 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 f48dd7ff32af..120f9c5908d1 100644
    --- a/fs/fuse/fuse_i.h
    +++ b/fs/fuse/fuse_i.h
    @@ -870,6 +870,13 @@ 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 93d28dc1f572..cf16d6d3a603 100644
    --- a/fs/fuse/inode.c
    +++ b/fs/fuse/inode.c
    @@ -350,8 +350,8 @@ retry:
    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 @@ retry:
    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;
    --
    2.30.2


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