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| author | Al Viro <viro@zeniv.linux.org.uk> | 2023-09-28 03:50:25 +0200 |
|---|---|---|
| committer | Al Viro <viro@zeniv.linux.org.uk> | 2024-02-25 08:10:31 +0100 |
| commit | 10a973fc4fb22390a8d362dd3265ec2c9a81d84c (patch) | |
| tree | 313c97a784a17d7aae0f338b95c63787572fbe87 /fs | |
| parent | afs: fix __afs_break_callback() / afs_drop_open_mmap() race (diff) | |
| download | linux-10a973fc4fb22390a8d362dd3265ec2c9a81d84c.tar.xz linux-10a973fc4fb22390a8d362dd3265ec2c9a81d84c.zip | |
nfs: make nfs_set_verifier() safe for use in RCU pathwalk
nfs_set_verifier() relies upon dentry being pinned; if that's
the case, grabbing ->d_lock stabilizes ->d_parent and guarantees
that ->d_parent points to a positive dentry. For something
we'd run into in RCU mode that is *not* true - dentry might've
been through dentry_kill() just as we grabbed ->d_lock, with
its parent going through the same just as we get to into
nfs_set_verifier_locked(). It might get to detaching inode
(and zeroing ->d_inode) before nfs_set_verifier_locked() gets
to fetching that; we get an oops as the result.
That can happen in nfs{,4} ->d_revalidate(); the call chain in
question is nfs_set_verifier_locked() <- nfs_set_verifier() <-
nfs_lookup_revalidate_delegated() <- nfs{,4}_do_lookup_revalidate().
We have checked that the parent had been positive, but that's
done before we get to nfs_set_verifier() and it's possible for
memory pressure to pick our dentry as eviction candidate by that
time. If that happens, back-to-back attempts to kill dentry and
its parent are quite normal. Sure, in case of eviction we'll
fail the ->d_seq check in the caller, but we need to survive
until we return there...
Acked-by: Christian Brauner <brauner@kernel.org>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Diffstat (limited to 'fs')
| -rw-r--r-- | fs/nfs/dir.c | 4 |
1 files changed, 2 insertions, 2 deletions
diff --git a/fs/nfs/dir.c b/fs/nfs/dir.c index c8ecbe999059..ac505671efbd 100644 --- a/fs/nfs/dir.c +++ b/fs/nfs/dir.c @@ -1431,9 +1431,9 @@ static bool nfs_verifier_is_delegated(struct dentry *dentry) static void nfs_set_verifier_locked(struct dentry *dentry, unsigned long verf) { struct inode *inode = d_inode(dentry); - struct inode *dir = d_inode(dentry->d_parent); + struct inode *dir = d_inode_rcu(dentry->d_parent); - if (!nfs_verify_change_attribute(dir, verf)) + if (!dir || !nfs_verify_change_attribute(dir, verf)) return; if (inode && NFS_PROTO(inode)->have_delegation(inode, FMODE_READ)) nfs_set_verifier_delegated(&verf); |