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author | Al Viro | 2023-09-27 21:50:25 -0400 |
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committer | Al Viro | 2024-02-25 02:10:31 -0500 |
commit | 10a973fc4fb22390a8d362dd3265ec2c9a81d84c (patch) | |
tree | 313c97a784a17d7aae0f338b95c63787572fbe87 /include | |
parent | 275655d3207b9e65d1561bf21c06a622d9ec1d43 (diff) |
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 'include')
0 files changed, 0 insertions, 0 deletions