dentry name snapshots (CVE-2017-7533)
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3341a33e22
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@ -23,6 +23,9 @@ linux (4.12.3-1~exp1) UNRELEASED; urgency=medium
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* debian/control: Fix version in dependencies on arch-independent
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linux-headers-*-common* (Closes: #869511)
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[ Salvatore Bonaccorso ]
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* dentry name snapshots (CVE-2017-7533)
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-- Ben Hutchings <ben@decadent.org.uk> Tue, 18 Jul 2017 13:26:41 +0100
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linux (4.12.2-1~exp1) experimental; urgency=medium
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@ -0,0 +1,242 @@
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From: Al Viro <viro@zeniv.linux.org.uk>
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Date: Fri, 7 Jul 2017 14:51:19 -0400
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Subject: dentry name snapshots
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Origin: https://git.kernel.org/linus/49d31c2f389acfe83417083e1208422b4091cd9e
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Bug-Debian-Security: https://security-tracker.debian.org/tracker/CVE-2017-7533
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take_dentry_name_snapshot() takes a safe snapshot of dentry name;
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if the name is a short one, it gets copied into caller-supplied
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structure, otherwise an extra reference to external name is grabbed
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(those are never modified). In either case the pointer to stable
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string is stored into the same structure.
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dentry must be held by the caller of take_dentry_name_snapshot(),
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but may be freely dropped afterwards - the snapshot will stay
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until destroyed by release_dentry_name_snapshot().
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Intended use:
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struct name_snapshot s;
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take_dentry_name_snapshot(&s, dentry);
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...
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access s.name
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...
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release_dentry_name_snapshot(&s);
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Replaces fsnotify_oldname_...(), gets used in fsnotify to obtain the name
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to pass down with event.
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Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
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---
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fs/dcache.c | 27 +++++++++++++++++++++++++++
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fs/debugfs/inode.c | 10 +++++-----
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fs/namei.c | 8 ++++----
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fs/notify/fsnotify.c | 8 ++++++--
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include/linux/dcache.h | 6 ++++++
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include/linux/fsnotify.h | 31 -------------------------------
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6 files changed, 48 insertions(+), 42 deletions(-)
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diff --git a/fs/dcache.c b/fs/dcache.c
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index b85da8897ffa..831f3a9a8f05 100644
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--- a/fs/dcache.c
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+++ b/fs/dcache.c
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@@ -277,6 +277,33 @@ static inline int dname_external(const struct dentry *dentry)
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return dentry->d_name.name != dentry->d_iname;
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}
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+void take_dentry_name_snapshot(struct name_snapshot *name, struct dentry *dentry)
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+{
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+ spin_lock(&dentry->d_lock);
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+ if (unlikely(dname_external(dentry))) {
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+ struct external_name *p = external_name(dentry);
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+ atomic_inc(&p->u.count);
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+ spin_unlock(&dentry->d_lock);
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+ name->name = p->name;
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+ } else {
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+ memcpy(name->inline_name, dentry->d_iname, DNAME_INLINE_LEN);
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+ spin_unlock(&dentry->d_lock);
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+ name->name = name->inline_name;
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+ }
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+}
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+EXPORT_SYMBOL(take_dentry_name_snapshot);
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+
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+void release_dentry_name_snapshot(struct name_snapshot *name)
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+{
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+ if (unlikely(name->name != name->inline_name)) {
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+ struct external_name *p;
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+ p = container_of(name->name, struct external_name, name[0]);
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+ if (unlikely(atomic_dec_and_test(&p->u.count)))
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+ kfree_rcu(p, u.head);
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+ }
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+}
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+EXPORT_SYMBOL(release_dentry_name_snapshot);
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+
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static inline void __d_set_inode_and_type(struct dentry *dentry,
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struct inode *inode,
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unsigned type_flags)
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diff --git a/fs/debugfs/inode.c b/fs/debugfs/inode.c
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index e892ae7d89f8..acd3be2cc691 100644
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--- a/fs/debugfs/inode.c
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+++ b/fs/debugfs/inode.c
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@@ -766,7 +766,7 @@ struct dentry *debugfs_rename(struct dentry *old_dir, struct dentry *old_dentry,
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{
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int error;
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struct dentry *dentry = NULL, *trap;
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- const char *old_name;
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+ struct name_snapshot old_name;
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trap = lock_rename(new_dir, old_dir);
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/* Source or destination directories don't exist? */
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@@ -781,19 +781,19 @@ struct dentry *debugfs_rename(struct dentry *old_dir, struct dentry *old_dentry,
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if (IS_ERR(dentry) || dentry == trap || d_really_is_positive(dentry))
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goto exit;
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- old_name = fsnotify_oldname_init(old_dentry->d_name.name);
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+ take_dentry_name_snapshot(&old_name, old_dentry);
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error = simple_rename(d_inode(old_dir), old_dentry, d_inode(new_dir),
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dentry, 0);
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if (error) {
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- fsnotify_oldname_free(old_name);
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+ release_dentry_name_snapshot(&old_name);
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goto exit;
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}
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d_move(old_dentry, dentry);
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- fsnotify_move(d_inode(old_dir), d_inode(new_dir), old_name,
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+ fsnotify_move(d_inode(old_dir), d_inode(new_dir), old_name.name,
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d_is_dir(old_dentry),
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NULL, old_dentry);
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- fsnotify_oldname_free(old_name);
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+ release_dentry_name_snapshot(&old_name);
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unlock_rename(new_dir, old_dir);
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dput(dentry);
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return old_dentry;
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diff --git a/fs/namei.c b/fs/namei.c
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index efe53a5d0737..c5588e837b15 100644
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--- a/fs/namei.c
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+++ b/fs/namei.c
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@@ -4362,11 +4362,11 @@ int vfs_rename(struct inode *old_dir, struct dentry *old_dentry,
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{
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int error;
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bool is_dir = d_is_dir(old_dentry);
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- const unsigned char *old_name;
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struct inode *source = old_dentry->d_inode;
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struct inode *target = new_dentry->d_inode;
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bool new_is_dir = false;
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unsigned max_links = new_dir->i_sb->s_max_links;
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+ struct name_snapshot old_name;
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if (source == target)
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return 0;
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@@ -4413,7 +4413,7 @@ int vfs_rename(struct inode *old_dir, struct dentry *old_dentry,
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if (error)
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return error;
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- old_name = fsnotify_oldname_init(old_dentry->d_name.name);
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+ take_dentry_name_snapshot(&old_name, old_dentry);
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dget(new_dentry);
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if (!is_dir || (flags & RENAME_EXCHANGE))
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lock_two_nondirectories(source, target);
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@@ -4468,14 +4468,14 @@ int vfs_rename(struct inode *old_dir, struct dentry *old_dentry,
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inode_unlock(target);
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dput(new_dentry);
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if (!error) {
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- fsnotify_move(old_dir, new_dir, old_name, is_dir,
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+ fsnotify_move(old_dir, new_dir, old_name.name, is_dir,
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!(flags & RENAME_EXCHANGE) ? target : NULL, old_dentry);
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if (flags & RENAME_EXCHANGE) {
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fsnotify_move(new_dir, old_dir, old_dentry->d_name.name,
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new_is_dir, NULL, new_dentry);
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}
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}
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- fsnotify_oldname_free(old_name);
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+ release_dentry_name_snapshot(&old_name);
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return error;
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}
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diff --git a/fs/notify/fsnotify.c b/fs/notify/fsnotify.c
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index 01a9f0f007d4..0c4583b61717 100644
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--- a/fs/notify/fsnotify.c
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+++ b/fs/notify/fsnotify.c
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@@ -161,16 +161,20 @@ int __fsnotify_parent(const struct path *path, struct dentry *dentry, __u32 mask
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if (unlikely(!fsnotify_inode_watches_children(p_inode)))
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__fsnotify_update_child_dentry_flags(p_inode);
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else if (p_inode->i_fsnotify_mask & mask) {
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+ struct name_snapshot name;
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+
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/* we are notifying a parent so come up with the new mask which
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* specifies these are events which came from a child. */
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mask |= FS_EVENT_ON_CHILD;
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+ take_dentry_name_snapshot(&name, dentry);
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if (path)
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ret = fsnotify(p_inode, mask, path, FSNOTIFY_EVENT_PATH,
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- dentry->d_name.name, 0);
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+ name.name, 0);
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else
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ret = fsnotify(p_inode, mask, dentry->d_inode, FSNOTIFY_EVENT_INODE,
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- dentry->d_name.name, 0);
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+ name.name, 0);
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+ release_dentry_name_snapshot(&name);
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}
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dput(parent);
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diff --git a/include/linux/dcache.h b/include/linux/dcache.h
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index d2e38dc6172c..025727bf6797 100644
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--- a/include/linux/dcache.h
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+++ b/include/linux/dcache.h
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@@ -591,5 +591,11 @@ static inline struct inode *d_real_inode(const struct dentry *dentry)
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return d_backing_inode(d_real((struct dentry *) dentry, NULL, 0));
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}
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+struct name_snapshot {
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+ const char *name;
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+ char inline_name[DNAME_INLINE_LEN];
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+};
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+void take_dentry_name_snapshot(struct name_snapshot *, struct dentry *);
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+void release_dentry_name_snapshot(struct name_snapshot *);
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#endif /* __LINUX_DCACHE_H */
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diff --git a/include/linux/fsnotify.h b/include/linux/fsnotify.h
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index b43d3f5bd9ea..b78aa7ac77ce 100644
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--- a/include/linux/fsnotify.h
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+++ b/include/linux/fsnotify.h
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@@ -293,35 +293,4 @@ static inline void fsnotify_change(struct dentry *dentry, unsigned int ia_valid)
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}
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}
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-#if defined(CONFIG_FSNOTIFY) /* notify helpers */
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-
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-/*
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- * fsnotify_oldname_init - save off the old filename before we change it
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- */
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-static inline const unsigned char *fsnotify_oldname_init(const unsigned char *name)
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-{
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- return kstrdup(name, GFP_KERNEL);
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-}
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-
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-/*
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- * fsnotify_oldname_free - free the name we got from fsnotify_oldname_init
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- */
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-static inline void fsnotify_oldname_free(const unsigned char *old_name)
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-{
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- kfree(old_name);
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-}
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-
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-#else /* CONFIG_FSNOTIFY */
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-
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-static inline const char *fsnotify_oldname_init(const unsigned char *name)
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-{
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- return NULL;
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-}
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-
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-static inline void fsnotify_oldname_free(const unsigned char *old_name)
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-{
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-}
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-
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-#endif /* CONFIG_FSNOTIFY */
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-
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#endif /* _LINUX_FS_NOTIFY_H */
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--
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2.11.0
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@ -117,6 +117,7 @@ features/all/lockdown/arm64-add-kernel-config-option-to-lock-down-when.patch
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# Security fixes
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debian/i386-686-pae-pci-set-pci-nobios-by-default.patch
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bugfix/all/dentry-name-snapshots.patch
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# Fix exported symbol versions
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bugfix/alpha/alpha-restore-symbol-versions-for-symbols-exported-f.patch
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