fuse: fix root lookup with nonzero generation

[ Upstream commit 68ca1b49e430f6534d0774a94147a823e3b8b26e ]

The root inode has a fixed nodeid and generation (1, 0).

Prior to the commit 15db16837a35 ("fuse: fix illegal access to inode with
reused nodeid") generation number on lookup was ignored.  After this commit
lookup with the wrong generation number resulted in the inode being
unhashed.  This is correct for non-root inodes, but replacing the root
inode is wrong and results in weird behavior.

Fix by reverting to the old behavior if ignoring the generation for the
root inode, but issuing a warning in dmesg.

Reported-by: Antonio SJ Musumeci <trapexit@spawn.link>
Closes: https://lore.kernel.org/all/CAOQ4uxhek5ytdN8Yz2tNEOg5ea4NkBb4nk0FGPjPk_9nz-VG3g@mail.gmail.com/
Fixes: 15db16837a35 ("fuse: fix illegal access to inode with reused nodeid")
Cc: <stable@vger.kernel.org> # v5.14
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>

diff --git a/fs/fuse/dir.c b/fs/fuse/dir.c
index 4ea52906ae150965c73a317e613ded339c189add..44d1c8cc58a42e36ee1b40deb635c276dce8e6e2 100644 (file)
--- a/fs/fuse/dir.c
+++ b/fs/fuse/dir.c
@@ -390,6 +390,10 @@ int fuse_lookup_name(struct super_block *sb, u64 nodeid, const struct qstr *name
                goto out_put_forget;
        if (fuse_invalid_attr(&outarg->attr))
                goto out_put_forget;
+       if (outarg->nodeid == FUSE_ROOT_ID && outarg->generation != 0) {
+               pr_warn_once("root generation should be zero\n");
+               outarg->generation = 0;
+       }
 
        *inode = fuse_iget(sb, outarg->nodeid, outarg->generation,
                           &outarg->attr, entry_attr_timeout(outarg),