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authorAl Viro <viro@zeniv.linux.org.uk>2023-09-27 21:50:25 -0400
committerAl Viro <viro@zeniv.linux.org.uk>2024-02-25 02:10:31 -0500
commit10a973fc4fb22390a8d362dd3265ec2c9a81d84c (patch)
tree313c97a784a17d7aae0f338b95c63787572fbe87
parent275655d3207b9e65d1561bf21c06a622d9ec1d43 (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>
-rw-r--r--fs/nfs/dir.c4
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);