linux-stable.git/fs/configfs, branch linux-4.9.y

configfs: fix a race in configfs_{,un}register_subsystem()

2022-03-02T10:32:03+00:00

[ Upstream commit 84ec758fb2daa236026506868c8796b0500c047d ]

When configfs_register_subsystem() or configfs_unregister_subsystem()
is executing link_group() or unlink_group(),
it is possible that two processes add or delete list concurrently.
Some unfortunate interleavings of them can cause kernel panic.

One of cases is:
A --> B --> C --> D
A <-- B <-- C <-- D

     delete list_head *B        |      delete list_head *C
--------------------------------|-----------------------------------
configfs_unregister_subsystem   |   configfs_unregister_subsystem
  unlink_group                  |     unlink_group
    unlink_obj                  |       unlink_obj
      list_del_init             |         list_del_init
        __list_del_entry        |           __list_del_entry
          __list_del            |             __list_del
            // next == C        |
            next->prev = prev   |
                                |               next->prev = prev
            prev->next = next   |
                                |                 // prev == B
                                |                 prev->next = next

Fix this by adding mutex when calling link_group() or unlink_group(),
but parent configfs_subsystem is NULL when config_item is root.
So I create a mutex configfs_subsystem_mutex.

Fixes: 7063fbf22611 ("[PATCH] configfs: User-driven configuration filesystem")
Signed-off-by: ChenXiaoSong 
Signed-off-by: Laibin Qiu 
Signed-off-by: Christoph Hellwig 
Signed-off-by: Sasha Levin

configfs: fix memleak in configfs_release_bin_file

2021-07-20T14:21:05+00:00

[ Upstream commit 3c252b087de08d3cb32468b54a158bd7ad0ae2f7 ]

When reading binary attributes in progress, buffer->bin_buffer is setup in
configfs_read_bin_file() but never freed.

Fixes: 03607ace807b4 ("configfs: implement binary attributes")
Signed-off-by: Chung-Chiang Cheng 
[hch: move the vfree rather than duplicating it]
Signed-off-by: Christoph Hellwig 
Signed-off-by: Sasha Levin

configfs: fix a use-after-free in __configfs_open_file

2021-03-17T15:10:18+00:00

[ Upstream commit 14fbbc8297728e880070f7b077b3301a8c698ef9 ]

Commit b0841eefd969 ("configfs: provide exclusion between IO and removals")
uses ->frag_dead to mark the fragment state, thus no bothering with extra
refcount on config_item when opening a file. The configfs_get_config_item
was removed in __configfs_open_file, but not with config_item_put. So the
refcount on config_item will lost its balance, causing use-after-free
issues in some occasions like this:

Test:
1. Mount configfs on /config with read-only items:
drwxrwx--- 289 root   root            0 2021-04-01 11:55 /config
drwxr-xr-x   2 root   root            0 2021-04-01 11:54 /config/a
--w--w--w-   1 root   root         4096 2021-04-01 11:53 /config/a/1.txt
......

2. Then run:
for file in /config
do
echo $file
grep -R 'key' $file
done

3. __configfs_open_file will be called in parallel, the first one
got called will do:
if (file->f_mode & FMODE_READ) {
	if (!(inode->i_mode & S_IRUGO))
		goto out_put_module;
			config_item_put(buffer->item);
				kref_put()
					package_details_release()
						kfree()

the other one will run into use-after-free issues like this:
BUG: KASAN: use-after-free in __configfs_open_file+0x1bc/0x3b0
Read of size 8 at addr fffffff155f02480 by task grep/13096
CPU: 0 PID: 13096 Comm: grep VIP: 00 Tainted: G        W       4.14.116-kasan #1
TGID: 13096 Comm: grep
Call trace:
dump_stack+0x118/0x160
kasan_report+0x22c/0x294
__asan_load8+0x80/0x88
__configfs_open_file+0x1bc/0x3b0
configfs_open_file+0x28/0x34
do_dentry_open+0x2cc/0x5c0
vfs_open+0x80/0xe0
path_openat+0xd8c/0x2988
do_filp_open+0x1c4/0x2fc
do_sys_open+0x23c/0x404
SyS_openat+0x38/0x48

Allocated by task 2138:
kasan_kmalloc+0xe0/0x1ac
kmem_cache_alloc_trace+0x334/0x394
packages_make_item+0x4c/0x180
configfs_mkdir+0x358/0x740
vfs_mkdir2+0x1bc/0x2e8
SyS_mkdirat+0x154/0x23c
el0_svc_naked+0x34/0x38

Freed by task 13096:
kasan_slab_free+0xb8/0x194
kfree+0x13c/0x910
package_details_release+0x524/0x56c
kref_put+0xc4/0x104
config_item_put+0x24/0x34
__configfs_open_file+0x35c/0x3b0
configfs_open_file+0x28/0x34
do_dentry_open+0x2cc/0x5c0
vfs_open+0x80/0xe0
path_openat+0xd8c/0x2988
do_filp_open+0x1c4/0x2fc
do_sys_open+0x23c/0x404
SyS_openat+0x38/0x48
el0_svc_naked+0x34/0x38

To fix this issue, remove the config_item_put in
__configfs_open_file to balance the refcount of config_item.

Fixes: b0841eefd969 ("configfs: provide exclusion between IO and removals")
Signed-off-by: Daiyue Zhang 
Signed-off-by: Yi Chen 
Signed-off-by: Ge Qiu 
Reviewed-by: Chao Yu 
Acked-by: Al Viro 
Signed-off-by: Christoph Hellwig 
Signed-off-by: Sasha Levin

configfs: fix config_item refcnt leak in configfs_rmdir()

2020-05-27T14:41:45+00:00

[ Upstream commit 8aebfffacfa379ba400da573a5bf9e49634e38cb ]

configfs_rmdir() invokes configfs_get_config_item(), which returns a
reference of the specified config_item object to "parent_item" with
increased refcnt.

When configfs_rmdir() returns, local variable "parent_item" becomes
invalid, so the refcount should be decreased to keep refcount balanced.

The reference counting issue happens in one exception handling path of
configfs_rmdir(). When down_write_killable() fails, the function forgets
to decrease the refcnt increased by configfs_get_config_item(), causing
a refcnt leak.

Fix this issue by calling config_item_put() when down_write_killable()
fails.

Signed-off-by: Xiyu Yang 
Signed-off-by: Xin Tan 
Signed-off-by: Christoph Hellwig 
Signed-off-by: Sasha Levin

configfs: fix a deadlock in configfs_symlink()

2019-11-12T18:15:51+00:00

commit 351e5d869e5ac10cb40c78b5f2d7dfc816ad4587 upstream.

Configfs abuses symlink(2).  Unlike the normal filesystems, it
wants the target resolved at symlink(2) time, like link(2) would've
done.  The problem is that ->symlink() is called with the parent
directory locked exclusive, so resolving the target inside the
->symlink() is easily deadlocked.

Short of really ugly games in sys_symlink() itself, all we can
do is to unlock the parent before resolving the target and
relock it after.  However, that invalidates the checks done
by the caller of ->symlink(), so we have to
	* check that dentry is still where it used to be
(it couldn't have been moved, but it could've been unhashed)
	* recheck that it's still negative (somebody else
might've successfully created a symlink with the same name
while we were looking the target up)
	* recheck the permissions on the parent directory.

Cc: stable@vger.kernel.org
Signed-off-by: Al Viro 
Signed-off-by: Christoph Hellwig 
Signed-off-by: Greg Kroah-Hartman

configfs: provide exclusion between IO and removals

2019-11-12T18:15:50+00:00

commit b0841eefd9693827afb9888235e26ddd098f9cef upstream.

Make sure that attribute methods are not called after the item
has been removed from the tree.  To do so, we
	* at the point of no return in removals, grab ->frag_sem
exclusive and mark the fragment dead.
	* call the methods of attributes with ->frag_sem taken
shared and only after having verified that the fragment is still
alive.

	The main benefit is for method instances - they are
guaranteed that the objects they are accessing *and* all ancestors
are still there.  Another win is that we don't need to bother
with extra refcount on config_item when opening a file -
the item will be alive for as long as it stays in the tree, and
we won't touch it/attributes/any associated data after it's
been removed from the tree.

Signed-off-by: Al Viro 
Signed-off-by: Christoph Hellwig 
Signed-off-by: Greg Kroah-Hartman

configfs: new object reprsenting tree fragments

2019-11-12T18:15:50+00:00

commit 47320fbe11a6059ae502c9c16b668022fdb4cf76 upstream.

Refcounted, hangs of configfs_dirent, created by operations that add
fragments to configfs tree (mkdir and configfs_register_{subsystem,group}).
Will be used in the next commit to provide exclusion between fragment
removal and ->show/->store calls.

Signed-off-by: Al Viro 
Signed-off-by: Christoph Hellwig 
Signed-off-by: Greg Kroah-Hartman

configfs_register_group() shouldn't be (and isn't) called in rmdirable parts

2019-11-12T18:15:49+00:00

commit f19e4ed1e1edbfa3c9ccb9fed17759b7d6db24c6 upstream.

revert cc57c07343bd "configfs: fix registered group removal"
It was an attempt to handle something that fundamentally doesn't
work - configfs_register_group() should never be done in a part
of tree that can be rmdir'ed.  And in mainline it never had been,
so let's not borrow trouble; the fix was racy anyway, it would take
a lot more to make that work and desired semantics is not clear.

Signed-off-by: Al Viro 
Signed-off-by: Christoph Hellwig 
Signed-off-by: Greg Kroah-Hartman

configfs: stash the data we need into configfs_buffer at open time

2019-11-12T18:15:49+00:00

commit ff4dd081977da56566a848f071aed8fa92d604a1 upstream.

simplifies the ->read()/->write()/->release() instances nicely

Signed-off-by: Al Viro 
Signed-off-by: Christoph Hellwig 
Signed-off-by: Greg Kroah-Hartman

configfs: Fix bool initialization/comparison

2019-11-12T18:15:48+00:00

commit 3f6928c347707a65cee10a9f54b85ad5fb078b3f upstream.

Bool initializations should use true and false. Bool tests don't need
comparisons.

Signed-off-by: Thomas Meyer 
Signed-off-by: Christoph Hellwig 
Signed-off-by: Greg Kroah-Hartman