[SRU][UNSTABLE/BIONIC/XENIAL][PATCH] UBUNTU: SAUCE: shiftfs: remove custom tmpfile method

[Christian Brauner]

BugLink: https://bugs.launchpad.net/bugs/1872757

Our revalidate methods were very opinionated about whether or not a
dentry was valid when we really should've just let the underlay tell us
what's what. This has led to bugs where a ESTALE was returned for e.g.
temporary files that were created and directly re-opened afterwards
through /proc/<pid>/fd/<nr-of-deleted-file>. When a file is re-opened
through /proc/<pid>/fd/<nr> LOOKUP_JUMP is set and the vfs will
revalidate via d_weak_revalidate(). Since the file has been unhashed or
even already gone negative we'd fail the open when we should've
succeeded.

I had also foolishly provided a .tmpfile method which so far only has
caused us trouble and which was involved in the ESTALE problem. If we
really need this then we can reimplement it properly but I doubt it.
Remove it for now.

Reported-by: Christian Kellner <ckellner at redhat.com>
Reported-by: Evgeny Vereshchagin >evvers at ya.ru>
Cc: Seth Forshee <seth.forshee at canonical.com>
Link: https://github.com/systemd/systemd/issues/14861
Signed-off-by: Christian Brauner <christian.brauner at ubuntu.com>
---
 fs/shiftfs.c | 45 +++++++++++++--------------------------------
 1 file changed, 13 insertions(+), 32 deletions(-)

diff --git a/fs/shiftfs.c b/fs/shiftfs.c
index 5c39529d0a17..39b878a6f820 100644
--- a/fs/shiftfs.c
+++ b/fs/shiftfs.c
@@ -240,19 +240,17 @@ static int shiftfs_d_weak_revalidate(struct dentry *dentry, unsigned int flags)
 	int err = 1;
 	struct dentry *lowerd = dentry->d_fsdata;
 
-	if (d_is_negative(lowerd) != d_is_negative(dentry))
-		return 0;
-
-	if ((lowerd->d_flags & DCACHE_OP_WEAK_REVALIDATE))
+	if (lowerd->d_flags & DCACHE_OP_WEAK_REVALIDATE) {
 		err = lowerd->d_op->d_weak_revalidate(lowerd, flags);
+		if (err < 0)
+			return err;
+	}
 
 	if (d_really_is_positive(dentry)) {
 		struct inode *inode = d_inode(dentry);
 		struct inode *loweri = d_inode(lowerd);
 
 		shiftfs_copyattr(loweri, inode);
-		if (!inode->i_nlink)
-			err = 0;
 	}
 
 	return err;
@@ -263,23 +261,25 @@ static int shiftfs_d_revalidate(struct dentry *dentry, unsigned int flags)
 	int err = 1;
 	struct dentry *lowerd = dentry->d_fsdata;
 
-	if (d_unhashed(lowerd) ||
-	    ((d_is_negative(lowerd) != d_is_negative(dentry))))
-		return 0;
-
 	if (flags & LOOKUP_RCU)
 		return -ECHILD;
 
-	if ((lowerd->d_flags & DCACHE_OP_REVALIDATE))
+	if (lowerd->d_flags & DCACHE_OP_REVALIDATE) {
 		err = lowerd->d_op->d_revalidate(lowerd, flags);
+		if (err < 0)
+			return err;
+		if (!err) {
+			if (!(flags & LOOKUP_RCU))
+				d_invalidate(lowerd);
+			return -ESTALE;
+		}
+	}
 
 	if (d_really_is_positive(dentry)) {
 		struct inode *inode = d_inode(dentry);
 		struct inode *loweri = d_inode(lowerd);
 
 		shiftfs_copyattr(loweri, inode);
-		if (!inode->i_nlink)
-			err = 0;
 	}
 
 	return err;
@@ -736,24 +736,6 @@ static int shiftfs_fiemap(struct inode *inode,
 	return err;
 }
 
-static int shiftfs_tmpfile(struct inode *dir, struct dentry *dentry,
-			   umode_t mode)
-{
-	int err;
-	const struct cred *oldcred;
-	struct dentry *lowerd = dentry->d_fsdata;
-	struct inode *loweri = dir->i_private;
-
-	if (!loweri->i_op->tmpfile)
-		return -EOPNOTSUPP;
-
-	oldcred = shiftfs_override_creds(dir->i_sb);
-	err = loweri->i_op->tmpfile(loweri, lowerd, mode);
-	revert_creds(oldcred);
-
-	return err;
-}
-
 static int shiftfs_setattr(struct dentry *dentry, struct iattr *attr)
 {
 	struct dentry *lowerd = dentry->d_fsdata;
@@ -1020,7 +1002,6 @@ static const struct inode_operations shiftfs_file_inode_operations = {
 	.listxattr	= shiftfs_listxattr,
 	.permission	= shiftfs_permission,
 	.setattr	= shiftfs_setattr,
-	.tmpfile	= shiftfs_tmpfile,
 };
 
 static const struct inode_operations shiftfs_special_inode_operations = {

base-commit: 1ff0ece4a5b555e1a72ec8d030b9410761174598
-- 
2.26.0