linux/fs/debugfs/inode.c, branch v4.7

Merge 4.6-rc4 into driver-core-next

2016-04-18T19:28:28Z

We want those fixes in here as well. Signed-off-by: Greg Kroah-Hartman

debugfs: Make automount point inodes permanently empty

2016-04-12T22:01:53Z

Starting with 4.1 the tracing subsystem has its own filesystem which is automounted in the tracing subdirectory of debugfs. Prior to this debugfs could be bind mounted in a cloned mount namespace, but if tracefs has been mounted under debugfs this now fails because there is a locked child mount. This creates a regression for container software which bind mounts debugfs to satisfy the assumption of some userspace software. In other pseudo filesystems such as proc and sysfs we're already creating mountpoints like this in such a way that no dirents can be created in the directories, allowing them to be exceptions to some MNT_LOCKED tests. In fact we're already do this for the tracefs mountpoint in sysfs. Do the same in debugfs_create_automount(), since the intention here is clearly to create a mountpoint. This fixes the regression, as locked child mounts on permanently empty directories do not cause a bind mount to fail. Cc: stable@vger.kernel.org # v4.1+ Signed-off-by: Seth Forshee Acked-by: Serge Hallyn Signed-off-by: Greg Kroah-Hartman

debugfs: add support for self-protecting attribute file fops

2016-04-12T21:14:21Z

In order to protect them against file removal issues, debugfs_create_file() creates a lifetime managing proxy around each struct file_operations handed in. In cases where this struct file_operations is able to manage file lifetime by itself already, the proxy created by debugfs is a waste of resources. The most common class of struct file_operations given to debugfs are those defined by means of the DEFINE_SIMPLE_ATTRIBUTE() macro. Introduce a DEFINE_DEBUGFS_ATTRIBUTE() macro to allow any struct file_operations of this class to be easily made file lifetime aware and thus, to be operated unproxied. Specifically, introduce debugfs_attr_read() and debugfs_attr_write() which wrap simple_attr_read() and simple_attr_write() under the protection of a debugfs_use_file_start()/debugfs_use_file_finish() pair. Make DEFINE_DEBUGFS_ATTRIBUTE() set the defined struct file_operations' ->read() and ->write() members to these wrappers. Export debugfs_create_file_unsafe() in order to allow debugfs users to create their files in non-proxying operation mode. Signed-off-by: Nicolai Stange Signed-off-by: Greg Kroah-Hartman

debugfs: prevent access to removed files' private data

2016-04-12T21:14:21Z

Upon return of debugfs_remove()/debugfs_remove_recursive(), it might still be attempted to access associated private file data through previously opened struct file objects. If that data has been freed by the caller of debugfs_remove*() in the meanwhile, the reading/writing process would either encounter a fault or, if the memory address in question has been reassigned again, unrelated data structures could get overwritten. However, since debugfs files are seldomly removed, usually from module exit handlers only, the impact is very low. Currently, there are ~1000 call sites of debugfs_create_file() spread throughout the whole tree and touching all of those struct file_operations in order to make them file removal aware by means of checking the result of debugfs_use_file_start() from within their methods is unfeasible. Instead, wrap the struct file_operations by a lifetime managing proxy at file open: - In debugfs_create_file(), the original fops handed in has got stashed away in ->d_fsdata already. - In debugfs_create_file(), install a proxy file_operations factory, debugfs_full_proxy_file_operations, at ->i_fop. This proxy factory has got an ->open() method only. It carries out some lifetime checks and if successful, dynamically allocates and sets up a new struct file_operations proxy at ->f_op. Afterwards, it forwards to the ->open() of the original struct file_operations in ->d_fsdata, if any. The dynamically set up proxy at ->f_op has got a lifetime managing wrapper set for each of the methods defined in the original struct file_operations in ->d_fsdata. Its ->release()er frees the proxy again and forwards to the original ->release(), if any. In order not to mislead the VFS layer, it is strictly necessary to leave those fields blank in the proxy that have been NULL in the original struct file_operations also, i.e. aren't supported. This is why there is a need for dynamically allocated proxies. The choice made not to allocate a proxy instance for every dentry at file creation, but for every struct file object instantiated thereof is justified by the expected usage pattern of debugfs, namely that in general very few files get opened more than once at a time. The wrapper methods set in the struct file_operations implement lifetime managing by means of the SRCU protection facilities already in place for debugfs: They set up a SRCU read side critical section and check whether the dentry is still alive by means of debugfs_use_file_start(). If so, they forward the call to the original struct file_operation stored in ->d_fsdata, still under the protection of the SRCU read side critical section. This SRCU read side critical section prevents any pending debugfs_remove() and friends to return to their callers. Since a file's private data must only be freed after the return of debugfs_remove(), the ongoing proxied call is guarded against any file removal race. If, on the other hand, the initial call to debugfs_use_file_start() detects that the dentry is dead, the wrapper simply returns -EIO and does not forward the call. Note that the ->poll() wrapper is special in that its signature does not allow for the return of arbitrary -EXXX values and thus, POLLHUP is returned here. In order not to pollute debugfs with wrapper definitions that aren't ever needed, I chose not to define a wrapper for every struct file_operations method possible. Instead, a wrapper is defined only for the subset of methods which are actually set by any debugfs users. Currently, these are: ->llseek() ->read() ->write() ->unlocked_ioctl() ->poll() The ->release() wrapper is special in that it does not protect the original ->release() in any way from dead files in order not to leak resources. Thus, any ->release() handed to debugfs must implement file lifetime management manually, if needed. For only 33 out of a total of 434 releasers handed in to debugfs, it could not be verified immediately whether they access data structures that might have been freed upon a debugfs_remove() return in the meanwhile. Export debugfs_use_file_start() and debugfs_use_file_finish() in order to allow any ->release() to manually implement file lifetime management. For a set of common cases of struct file_operations implemented by the debugfs_core itself, future patches will incorporate file lifetime management directly within those in order to allow for their unproxied operation. Rename the original, non-proxying "debugfs_create_file()" to "debugfs_create_file_unsafe()" and keep it for future internal use by debugfs itself. Factor out code common to both into the new __debugfs_create_file(). Signed-off-by: Nicolai Stange Signed-off-by: Greg Kroah-Hartman

debugfs: prevent access to possibly dead file_operations at file open

2016-04-12T21:14:21Z

Nothing prevents a dentry found by path lookup before a return of __debugfs_remove() to actually get opened after that return. Now, after the return of __debugfs_remove(), there are no guarantees whatsoever regarding the memory the corresponding inode's file_operations object had been kept in. Since __debugfs_remove() is seldomly invoked, usually from module exit handlers only, the race is hard to trigger and the impact is very low. A discussion of the problem outlined above as well as a suggested solution can be found in the (sub-)thread rooted at http://lkml.kernel.org/g/20130401203445.GA20862@ZenIV.linux.org.uk ("Yet another pipe related oops.") Basically, Greg KH suggests to introduce an intermediate fops and Al Viro points out that a pointer to the original ones may be stored in ->d_fsdata. Follow this line of reasoning: - Add SRCU as a reverse dependency of DEBUG_FS. - Introduce a srcu_struct object for the debugfs subsystem. - In debugfs_create_file(), store a pointer to the original file_operations object in ->d_fsdata. - Make debugfs_remove() and debugfs_remove_recursive() wait for a SRCU grace period after the dentry has been delete()'d and before they return to their callers. - Introduce an intermediate file_operations object named "debugfs_open_proxy_file_operations". It's ->open() functions checks, under the protection of a SRCU read lock, whether the dentry is still alive, i.e. has not been d_delete()'d and if so, tries to acquire a reference on the owning module. On success, it sets the file object's ->f_op to the original file_operations and forwards the ongoing open() call to the original ->open(). - For clarity, rename the former debugfs_file_operations to debugfs_noop_file_operations -- they are in no way canonical. The choice of SRCU over "normal" RCU is justified by the fact, that the former may also be used to protect ->i_private data from going away during the execution of a file's readers and writers which may (and do) sleep. Finally, introduce the fs/debugfs/internal.h header containing some declarations internal to the debugfs implementation. Signed-off-by: Nicolai Stange Signed-off-by: Greg Kroah-Hartman

fs: debugfs: Replace CURRENT_TIME by current_fs_time()

2016-03-29T17:11:44Z

CURRENT_TIME macro is not appropriate for filesystems as it doesn't use the right granularity for filesystem timestamps. Use current_fs_time() instead. Signed-off-by: Deepa Dinamani Signed-off-by: Greg Kroah-Hartman

debugfs: fix inode i_nlink references for automount dentry

2016-03-29T17:11:44Z

Directory inodes should start off with i_nlink == 2 (one extra ref for "." entry). debugfs_create_automount() increases neither the i_nlink reference for current inode nor for parent inode. On attempt to remove the automount dentry, kernel complains: [ 86.288070] WARNING: CPU: 1 PID: 3616 at fs/inode.c:273 drop_nlink+0x3e/0x50() [ 86.288461] Modules linked in: debugfs_example2(O-) [ 86.288745] CPU: 1 PID: 3616 Comm: rmmod Tainted: G O 4.4.0-rc3-next-20151207+ #135 [ 86.289197] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.8.2-20150617_082717-anatol 04/01/2014 [ 86.289696] ffffffff81be05c9 ffff8800b9e6fda0 ffffffff81352e2c 0000000000000000 [ 86.290110] ffff8800b9e6fdd8 ffffffff81065142 ffff8801399175e8 ffff8800bb78b240 [ 86.290507] ffff8801399175e8 ffff8800b73d7898 ffff8800b73d7840 ffff8800b9e6fde8 [ 86.290933] Call Trace: [ 86.291080] [] dump_stack+0x4e/0x82 [ 86.291340] [] warn_slowpath_common+0x82/0xc0 [ 86.291640] [] warn_slowpath_null+0x1a/0x20 [ 86.291932] [] drop_nlink+0x3e/0x50 [ 86.292208] [] simple_unlink+0x4b/0x60 [ 86.292481] [] simple_rmdir+0x37/0x50 [ 86.292748] [] __debugfs_remove.part.16+0xa8/0xd0 [ 86.293082] [] debugfs_remove_recursive+0xdb/0x1c0 [ 86.293406] [] cleanup_module+0x2d/0x3b [debugfs_example2] [ 86.293762] [] SyS_delete_module+0x16b/0x220 [ 86.294077] [] entry_SYSCALL_64_fastpath+0x12/0x6a [ 86.294405] ---[ end trace c9fc53353fe14a36 ]--- [ 86.294639] ------------[ cut here ]------------ To reproduce the issue it is enough to invoke these lines: autom = debugfs_create_automount("automount", NULL, vfsmount_cb, data); BUG_ON(IS_ERR_OR_NULL(autom)); debugfs_remove(autom); The issue is fixed by increasing inode i_nlink references for current and parent inodes. Signed-off-by: Roman Pen Signed-off-by: Greg Kroah-Hartman

wrappers for ->i_mutex access

2016-01-22T23:04:28Z

parallel to mutex_{lock,unlock,trylock,is_locked,lock_nested}, inode_foo(inode) being mutex_foo(&inode->i_mutex). Please, use those for access to ->i_mutex; over the coming cycle ->i_mutex will become rwsem, with ->lookup() done with it held only shared. Signed-off-by: Al Viro

debugfs: fix refcount imbalance in start_creating

2015-11-11T07:04:44Z

In debugfs' start_creating(), we pin the file system to safely access its root. When we failed to create a file, we unpin the file system via failed_creating() to release the mount count and eventually the reference of the vfsmount. However, when we run into an error during lookup_one_len() when still in start_creating(), we only release the parent's mutex but not so the reference on the mount. Looks like it was done in the past, but after splitting portions of __create_file() into start_creating() and end_creating() via 190afd81e4a5 ("debugfs: split the beginning and the end of __create_file() off"), this seemed missed. Noticed during code review. Fixes: 190afd81e4a5 ("debugfs: split the beginning and the end of __create_file() off") Cc: stable@vger.kernel.org # v4.0+ Signed-off-by: Daniel Borkmann Signed-off-by: Al Viro

debugfs: document that debugfs_remove*() accepts NULL and error values

2015-10-04T10:36:07Z

According to commit a59d6293e537 ("debugfs: change parameter check in debugfs_remove() functions"), this is meant to make cleanup easier for callers. In that case it ought to be documented. Signed-off-by: Ulf Magnusson Signed-off-by: Greg Kroah-Hartman