From: Al Viro <viro@zeniv.linux.org.uk>
To: linux-fsdevel@vger.kernel.org
Cc: Ritesh Harjani <riteshh@linux.ibm.com>,
linux-kernel@vger.kernel.org, wugyuan@cn.ibm.com,
jlayton@kernel.org, hsiangkao@aol.com, Jan Kara <jack@suse.cz>,
Linus Torvalds <torvalds@linux-foundation.org>,
ecryptfs@vger.kernel.org
Subject: [PATCH][RFC] ecryptfs_lookup_interpose(): lower_dentry->d_inode is not stable
Date: Sun, 3 Nov 2019 18:51:33 +0000 [thread overview]
Message-ID: <20191103185133.GR26530@ZenIV.linux.org.uk> (raw)
In-Reply-To: <20191103182058.GQ26530@ZenIV.linux.org.uk>
lower_dentry can't go from positive to negative (we have it pinned),
but it *can* go from negative to positive. So fetching ->d_inode
into a local variable, doing a blocking allocation, checking that
now ->d_inode is non-NULL and feeding the value we'd fetched
earlier to a function that won't accept NULL is not a good idea.
Cc: stable@vger.kernel.org
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
---
diff --git a/fs/ecryptfs/inode.c b/fs/ecryptfs/inode.c
index a905d5f4f3b0..3c2298721359 100644
--- a/fs/ecryptfs/inode.c
+++ b/fs/ecryptfs/inode.c
@@ -319,7 +319,7 @@ static int ecryptfs_i_size_read(struct dentry *dentry, struct inode *inode)
static struct dentry *ecryptfs_lookup_interpose(struct dentry *dentry,
struct dentry *lower_dentry)
{
- struct inode *inode, *lower_inode = d_inode(lower_dentry);
+ struct inode *inode, *lower_inode;
struct ecryptfs_dentry_info *dentry_info;
struct vfsmount *lower_mnt;
int rc = 0;
@@ -339,7 +339,15 @@ static struct dentry *ecryptfs_lookup_interpose(struct dentry *dentry,
dentry_info->lower_path.mnt = lower_mnt;
dentry_info->lower_path.dentry = lower_dentry;
- if (d_really_is_negative(lower_dentry)) {
+ /*
+ * negative dentry can go positive under us here - its parent is not
+ * locked. That's OK and that could happen just as we return from
+ * ecryptfs_lookup() anyway. Just need to be careful and fetch
+ * ->d_inode only once - it's not stable here.
+ */
+ lower_inode = READ_ONCE(lower_dentry->d_inode);
+
+ if (!lower_inode) {
/* We want to add because we couldn't find in lower */
d_add(dentry, NULL);
return NULL;
next prev parent reply other threads:[~2019-11-03 18:51 UTC|newest]
Thread overview: 26+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-09-27 4:42 [PATCH RESEND 1/1] vfs: Really check for inode ptr in lookup_fast Ritesh Harjani
2019-10-15 4:07 ` Ritesh Harjani
2019-10-22 13:38 ` Ritesh Harjani
2019-10-22 14:37 ` Al Viro
2019-10-22 14:50 ` Al Viro
2019-10-22 20:11 ` Al Viro
2019-10-23 11:05 ` Ritesh Harjani
2019-11-01 23:46 ` Al Viro
2019-11-02 6:17 ` Al Viro
2019-11-02 17:24 ` Paul E. McKenney
2019-11-02 17:22 ` Paul E. McKenney
2019-11-02 18:08 ` Al Viro
2019-11-03 14:41 ` Paul E. McKenney
2019-11-03 16:35 ` [RFC] lookup_one_len_unlocked() lousy calling conventions Al Viro
2019-11-03 18:20 ` Al Viro
2019-11-03 18:51 ` Al Viro [this message]
2019-11-03 19:03 ` [PATCH][RFC] ecryptfs_lookup_interpose(): lower_dentry->d_parent is not stable either Al Viro
2019-11-13 7:01 ` [PATCH][RFC] ecryptfs_lookup_interpose(): lower_dentry->d_inode is not stable Amir Goldstein
2019-11-13 12:52 ` Al Viro
2019-11-13 16:22 ` Amir Goldstein
2019-11-13 20:18 ` Jean-Louis Biasini
2019-11-03 17:05 ` [PATCH][RFC] ecryptfs unlink/rmdir breakage (similar to caught in ecryptfs rename last year) Al Viro
2019-11-09 3:13 ` [PATCH][RFC] race in exportfs_decode_fh() Al Viro
2019-11-09 16:55 ` Linus Torvalds
2019-11-09 18:26 ` Al Viro
2019-11-11 9:16 ` Christoph Hellwig
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