Apparently, there are some applications that use IN_DELETE event as an invalidation mechanism and expect that if they try to open a file with the name reported with the delete event, that it should not contain the content of the deleted file.

Commit 49246466a989 ("fsnotify: move fsnotify_nameremove() hook out of d_delete()") moved the fsnotify delete hook before d_delete() so fsnotify will have access to a positive dentry.

This allowed a race where opening the deleted file via cached dentry is now possible after receiving the IN_DELETE event.

To fix the regression, we use two different techniques: 1) For call sites that call d_delete() with elevated refcount, convert the call to d_drop() and move the fsnotify hook after d_drop(). 2) For the vfs helpers that may turn dentry to negative on d_delete(), use a helper d_delete_notify() to pin the inode, so we can pass it to an fsnotify hook after d_delete().

Create a new hook fsnotify_delete() that allows to pass a negative dentry and takes the unlinked inode as an argument.

Add a missing fsnotify_unlink() hook in nfsdfs that was found during the call sites audit.

Note that the call sites in simple_recursive_removal() follow d_invalidate(), so they require no change.

Backporting hint: this regression is from v5.3. Although patch will apply with only trivial conflicts to v5.4 and v5.10, it won't build, because fsnotify_delete() implementation is different in each of those versions (see fsnotify_link()).

Reported-by: Ivan Delalande colona@arista.com Link: https://lore.kernel.org/linux-fsdevel/YeNyzoDM5hP5LtGW@visor/ Fixes: 49246466a989 ("fsnotify: move fsnotify_nameremove() hook out of d_delete()") Cc: stable@vger.kernel.org # v5.3+ Signed-off-by: Amir Goldstein amir73il@gmail.com ---

Jan,

This turned into an audit of fsnotify_unlink/rmdir() call sites, so besides fixing the regression, I also added one missing hook and replaced most of the d_delete() calls with d_drop() to simplify things.

I will follow up with backports for v5.4 and v5.10 and will send the repro to LTP guys.

Thanks, Amir.

fs/btrfs/ioctl.c | 5 ++--- fs/configfs/dir.c | 6 +++--- fs/devpts/inode.c | 2 +- fs/namei.c | 27 ++++++++++++++++++++++----- fs/nfsd/nfsctl.c | 5 +++-- include/linux/fsnotify.h | 20 ++++++++++++++++++++ net/sunrpc/rpc_pipe.c | 4 ++-- 7 files changed, 53 insertions(+), 16 deletions(-)

diff --git a/fs/btrfs/ioctl.c b/fs/btrfs/ioctl.c index edfecfe62b4b..121e8f439996 100644 --- a/fs/btrfs/ioctl.c +++ b/fs/btrfs/ioctl.c @@ -3060,10 +3060,9 @@ static noinline int btrfs_ioctl_snap_destroy(struct file *file, btrfs_inode_lock(inode, 0); err = btrfs_delete_subvolume(dir, dentry); btrfs_inode_unlock(inode, 0); - if (!err) { + d_drop(dentry); + if (!err) fsnotify_rmdir(dir, dentry); - d_delete(dentry); - }

out_dput: dput(dentry); diff --git a/fs/configfs/dir.c b/fs/configfs/dir.c index 1466b5d01cbb..d3cd2a94d1e8 100644 --- a/fs/configfs/dir.c +++ b/fs/configfs/dir.c @@ -1780,8 +1780,8 @@ void configfs_unregister_group(struct config_group *group) configfs_detach_group(&group->cg_item); d_inode(dentry)->i_flags |= S_DEAD; dont_mount(dentry); + d_drop(dentry); fsnotify_rmdir(d_inode(parent), dentry); - d_delete(dentry); inode_unlock(d_inode(parent));

dput(dentry); @@ -1922,10 +1922,10 @@ void configfs_unregister_subsystem(struct configfs_subsystem *subsys) configfs_detach_group(&group->cg_item); d_inode(dentry)->i_flags |= S_DEAD; dont_mount(dentry); - fsnotify_rmdir(d_inode(root), dentry); inode_unlock(d_inode(dentry));

- d_delete(dentry); + d_drop(dentry); + fsnotify_rmdir(d_inode(root), dentry);

inode_unlock(d_inode(root));

diff --git a/fs/devpts/inode.c b/fs/devpts/inode.c index 42e5a766d33c..4f25015aa534 100644 --- a/fs/devpts/inode.c +++ b/fs/devpts/inode.c @@ -621,8 +621,8 @@ void devpts_pty_kill(struct dentry *dentry)

dentry->d_fsdata = NULL; drop_nlink(dentry->d_inode); - fsnotify_unlink(d_inode(dentry->d_parent), dentry); d_drop(dentry); + fsnotify_unlink(d_inode(dentry->d_parent), dentry); dput(dentry); /* d_alloc_name() in devpts_pty_new() */ }

diff --git a/fs/namei.c b/fs/namei.c index 1f9d2187c765..b11991b57f9b 100644 --- a/fs/namei.c +++ b/fs/namei.c @@ -3929,6 +3929,23 @@ SYSCALL_DEFINE2(mkdir, const char __user *, pathname, umode_t, mode) return do_mkdirat(AT_FDCWD, getname(pathname), mode); }

+/** + * d_delete_notify - delete a dentry and call fsnotify_delete() + * @dentry: The dentry to delete + * + * This helper is used to guaranty that the unlinked inode cannot be found + * by lookup of this name after fsnotify_delete() event has been delivered. + */ +static void d_delete_notify(struct inode *dir, struct dentry *dentry) +{ + struct inode *inode = d_inode(dentry); + + ihold(inode); + d_delete(dentry); + fsnotify_delete(dir, inode, dentry); + iput(inode); +} + /** * vfs_rmdir - remove directory * @mnt_userns: user namespace of the mount the inode was found from @@ -3973,13 +3990,12 @@ int vfs_rmdir(struct user_namespace *mnt_userns, struct inode *dir, dentry->d_inode->i_flags |= S_DEAD; dont_mount(dentry); detach_mounts(dentry); - fsnotify_rmdir(dir, dentry);

out: inode_unlock(dentry->d_inode); dput(dentry); if (!error) - d_delete(dentry); + d_delete_notify(dir, dentry); return error; } EXPORT_SYMBOL(vfs_rmdir); @@ -4101,7 +4117,6 @@ int vfs_unlink(struct user_namespace *mnt_userns, struct inode *dir, if (!error) { dont_mount(dentry); detach_mounts(dentry); - fsnotify_unlink(dir, dentry); } } } @@ -4109,9 +4124,11 @@ int vfs_unlink(struct user_namespace *mnt_userns, struct inode *dir, inode_unlock(target);

/* We don't d_delete() NFS sillyrenamed files--they still exist. */ - if (!error && !(dentry->d_flags & DCACHE_NFSFS_RENAMED)) { + if (dentry->d_flags & DCACHE_NFSFS_RENAMED) { + fsnotify_unlink(dir, dentry); + } else if (!error) { fsnotify_link_count(target); - d_delete(dentry); + d_delete_notify(dir, dentry); }

return error; diff --git a/fs/nfsd/nfsctl.c b/fs/nfsd/nfsctl.c index 51a49e0cfe37..d0761ca8cb54 100644 --- a/fs/nfsd/nfsctl.c +++ b/fs/nfsd/nfsctl.c @@ -1249,7 +1249,8 @@ static void nfsdfs_remove_file(struct inode *dir, struct dentry *dentry) clear_ncl(d_inode(dentry)); dget(dentry); ret = simple_unlink(dir, dentry); - d_delete(dentry); + d_drop(dentry); + fsnotify_unlink(dir, dentry); dput(dentry); WARN_ON_ONCE(ret); } @@ -1340,8 +1341,8 @@ void nfsd_client_rmdir(struct dentry *dentry) dget(dentry); ret = simple_rmdir(dir, dentry); WARN_ON_ONCE(ret); + d_drop(dentry); fsnotify_rmdir(dir, dentry); - d_delete(dentry); dput(dentry); inode_unlock(dir); } diff --git a/include/linux/fsnotify.h b/include/linux/fsnotify.h index 3a2d7dc3c607..b4a4085adc89 100644 --- a/include/linux/fsnotify.h +++ b/include/linux/fsnotify.h @@ -224,6 +224,26 @@ static inline void fsnotify_link(struct inode *dir, struct inode *inode, dir, &new_dentry->d_name, 0); }

+/* + * fsnotify_delete - @dentry was unlinked and unhashed + * + * Caller must make sure that dentry->d_name is stable. + * + * Note: unlike fsnotify_unlink(), we have to pass also the unlinked inode + * as this may be called after d_delete() and old_dentry may be negative. + */ +static inline void fsnotify_delete(struct inode *dir, struct inode *inode, + struct dentry *dentry) +{ + __u32 mask = FS_DELETE; + + if (S_ISDIR(inode->i_mode)) + mask |= FS_ISDIR; + + fsnotify_name(mask, inode, FSNOTIFY_EVENT_INODE, dir, &dentry->d_name, + 0); +} + /* * fsnotify_unlink - 'name' was unlinked * diff --git a/net/sunrpc/rpc_pipe.c b/net/sunrpc/rpc_pipe.c index ee5336d73fdd..35588f0afa86 100644 --- a/net/sunrpc/rpc_pipe.c +++ b/net/sunrpc/rpc_pipe.c @@ -600,9 +600,9 @@ static int __rpc_rmdir(struct inode *dir, struct dentry *dentry)

dget(dentry); ret = simple_rmdir(dir, dentry); + d_drop(dentry); if (!ret) fsnotify_rmdir(dir, dentry); - d_delete(dentry); dput(dentry); return ret; } @@ -613,9 +613,9 @@ static int __rpc_unlink(struct inode *dir, struct dentry *dentry)

dget(dentry); ret = simple_unlink(dir, dentry); + d_drop(dentry); if (!ret) fsnotify_unlink(dir, dentry); - d_delete(dentry); dput(dentry); return ret; }