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From: Al Viro <viro@zeniv.linux.org.uk>
To: linux-fsdevel@vger.kernel.org
Cc: Linus Torvalds <torvalds@linux-foundation.org>,
	Christian Brauner <brauner@kernel.org>,
	linux-ext4@vger.kernel.org, linux-nfs@vger.kernel.org,
	Miklos Szeredi <miklos@szeredi.hu>,
	linux-cifs@vger.kernel.org
Subject: [PATCH 07/13] nfs: make nfs_set_verifier() safe for use in RCU pathwalk
Date: Sun,  4 Feb 2024 02:17:33 +0000	[thread overview]
Message-ID: <20240204021739.1157830-7-viro@zeniv.linux.org.uk> (raw)
In-Reply-To: <20240204021739.1157830-1-viro@zeniv.linux.org.uk>

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...

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
---
 fs/nfs/dir.c | 4 ++--
 1 file 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);
-- 
2.39.2


  parent reply	other threads:[~2024-02-04  2:17 UTC|newest]

Thread overview: 36+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2024-02-04  2:14 [PATCHES] RCU pathwalk race fixes Al Viro
2024-02-04  2:17 ` [PATCH 01/13] fs/super.c: don't drop ->s_user_ns until we free struct super_block itself Al Viro
2024-02-04  2:17   ` [PATCH 02/13] rcu pathwalk: prevent bogus hard errors from may_lookup() Al Viro
2024-02-05 12:26     ` Christian Brauner
2024-02-04  2:17   ` [PATCH 03/13] affs: free affs_sb_info with kfree_rcu() Al Viro
2024-02-05 12:26     ` Christian Brauner
2024-02-04  2:17   ` [PATCH 04/13] exfat: move freeing sbi, upcase table and dropping nls into rcu-delayed helper Al Viro
2024-02-05 12:27     ` Christian Brauner
2024-02-04  2:17   ` [PATCH 05/13] hfsplus: switch to rcu-delayed unloading of nls and freeing ->s_fs_info Al Viro
2024-02-05 12:27     ` Christian Brauner
2024-02-04  2:17   ` [PATCH 06/13] afs: fix __afs_break_callback() / afs_drop_open_mmap() race Al Viro
2024-02-05 12:28     ` Christian Brauner
2024-02-04  2:17   ` Al Viro [this message]
2024-02-05 12:29     ` [PATCH 07/13] nfs: make nfs_set_verifier() safe for use in RCU pathwalk Christian Brauner
2024-02-04  2:17   ` [PATCH 08/13] nfs: fix UAF on pathwalk running into umount Al Viro
2024-02-05 12:29     ` Christian Brauner
2024-02-04  2:17   ` [PATCH 09/13] procfs: move dropping pde and pid from ->evict_inode() to ->free_inode() Al Viro
2024-02-05 12:30     ` Christian Brauner
2024-02-04  2:17   ` [PATCH 10/13] procfs: make freeing proc_fs_info rcu-delayed Al Viro
2024-02-05 12:31     ` Christian Brauner
2024-02-04  2:17   ` [PATCH 11/13] fuse: fix UAF in rcu pathwalks Al Viro
2024-02-05 12:31     ` Christian Brauner
2024-02-05 13:51       ` Miklos Szeredi
2024-03-04 14:36         ` Amir Goldstein
2024-03-05 12:43           ` Miklos Szeredi
2024-03-06 10:18             ` Amir Goldstein
2024-03-06 10:21               ` Miklos Szeredi
2024-02-04  2:17   ` [PATCH 12/13] cifs_get_link(): bail out in unsafe case Al Viro
2024-02-04 15:45     ` Steve French
2024-02-04 16:25       ` Al Viro
2024-02-04 16:41         ` Al Viro
2024-02-04  2:17   ` [PATCH 13/13] ext4_get_link(): fix breakage in RCU mode Al Viro
2024-02-05 12:24   ` [PATCH 01/13] fs/super.c: don't drop ->s_user_ns until we free struct super_block itself Christian Brauner
2024-02-05 12:36   ` Jeff Layton
2024-02-04  2:27 ` RCU pathwalk audit notes Al Viro
2024-02-05 12:48 ` [PATCHES] RCU pathwalk race fixes Jeff Layton

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