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 a4ad01a78e82677f7b8ab37d48d0ea215676d2b3..a8a7fc0e1754776e0b86bc64c2dc3d8bae2d059b 100644 (file)
--- a/fs/fuse/dir.c
+++ b/fs/fuse/dir.c
@@ -391,6 +391,10 @@ int fuse_lookup_name(struct super_block *sb, u64 nodeid, const struct qstr *name
        err = -EIO;
        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, ATTR_TIMEOUT(outarg),