linux-stable.git/fs/cachefiles, branch v4.9.232

cachefiles: Fix race between read_waiter and read_copier involving op->to_do

2020-06-03T06:16:36+00:00

[ Upstream commit 7bb0c5338436dae953622470d52689265867f032 ]

There is a potential race in fscache operation enqueuing for reading and
copying multiple pages from cachefiles to netfs.  The problem can be seen
easily on a heavy loaded system (for example many processes reading files
continually on an NFS share covered by fscache triggered this problem within
a few minutes).

The race is due to cachefiles_read_waiter() adding the op to the monitor
to_do list and then then drop the object->work_lock spinlock before
completing fscache_enqueue_operation().  Once the lock is dropped,
cachefiles_read_copier() grabs the op, completes processing it, and
makes it through fscache_retrieval_complete() which sets the op->state to
the final state of FSCACHE_OP_ST_COMPLETE(4).  When cachefiles_read_waiter()
finally gets through the remainder of fscache_enqueue_operation()
it sees the invalid state, and hits the ASSERTCMP and the following
oops is seen:
[ 2259.612361] FS-Cache:
[ 2259.614785] FS-Cache: Assertion failed
[ 2259.618639] FS-Cache: 4 == 5 is false
[ 2259.622456] ------------[ cut here ]------------
[ 2259.627190] kernel BUG at fs/fscache/operation.c:70!
...
[ 2259.791675] RIP: 0010:[]  [] fscache_enqueue_operation+0xff/0x170 [fscache]
[ 2259.802059] RSP: 0000:ffffa0263d543be0  EFLAGS: 00010046
[ 2259.807521] RAX: 0000000000000019 RBX: ffffa01a4d390480 RCX: 0000000000000006
[ 2259.814847] RDX: 0000000000000000 RSI: 0000000000000046 RDI: ffffa0263d553890
[ 2259.822176] RBP: ffffa0263d543be8 R08: 0000000000000000 R09: ffffa0263c2d8708
[ 2259.829502] R10: 0000000000001e7f R11: 0000000000000000 R12: ffffa01a4d390480
[ 2259.844483] R13: ffff9fa9546c5920 R14: ffffa0263d543c80 R15: ffffa0293ff9bf10
[ 2259.859554] FS:  00007f4b6efbd700(0000) GS:ffffa0263d540000(0000) knlGS:0000000000000000
[ 2259.875571] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[ 2259.889117] CR2: 00007f49e1624ff0 CR3: 0000012b38b38000 CR4: 00000000007607e0
[ 2259.904015] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
[ 2259.918764] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
[ 2259.933449] PKRU: 55555554
[ 2259.943654] Call Trace:
[ 2259.953592]  
[ 2259.955577]  [] cachefiles_read_waiter+0x92/0xf0 [cachefiles]
[ 2259.978039]  [] __wake_up_common+0x82/0x120
[ 2259.991392]  [] __wake_up_common_lock+0x83/0xc0
[ 2260.004930]  [] ? task_rq_unlock+0x20/0x20
[ 2260.017863]  [] __wake_up+0x13/0x20
[ 2260.030230]  [] __wake_up_bit+0x50/0x70
[ 2260.042535]  [] unlock_page+0x2b/0x30
[ 2260.054495]  [] page_endio+0x29/0x90
[ 2260.066184]  [] mpage_end_io+0x51/0x80

CPU1
cachefiles_read_waiter()
 20 static int cachefiles_read_waiter(wait_queue_entry_t *wait, unsigned mode,
 21                                   int sync, void *_key)
 22 {
...
 61         spin_lock(&object->work_lock);
 62         list_add_tail(&monitor->op_link, &op->to_do);
 63         spin_unlock(&object->work_lock);

 64
 65         fscache_enqueue_retrieval(op);
182 static inline void fscache_enqueue_retrieval(struct fscache_retrieval *op)
183 {
184         fscache_enqueue_operation(&op->op);
185 }
 58 void fscache_enqueue_operation(struct fscache_operation *op)
 59 {
 60         struct fscache_cookie *cookie = op->object->cookie;
 61
 62         _enter("{OBJ%x OP%x,%u}",
 63                op->object->debug_id, op->debug_id, atomic_read(&op->usage));
 64
 65         ASSERT(list_empty(&op->pend_link));
 66         ASSERT(op->processor != NULL);
 67         ASSERT(fscache_object_is_available(op->object));
 68         ASSERTCMP(atomic_read(&op->usage), >, 0);


CPU2
cachefiles_read_copier()
168         while (!list_empty(&op->to_do)) {
...
202                 fscache_end_io(op, monitor->netfs_page, error);
203                 put_page(monitor->netfs_page);
204                 fscache_retrieval_complete(op, 1);

CPU1
 58 void fscache_enqueue_operation(struct fscache_operation *op)
 59 {
...
 69         ASSERTIFCMP(op->state != FSCACHE_OP_ST_IN_PROGRESS,
 70                     op->state, ==,  FSCACHE_OP_ST_CANCELLED);

Signed-off-by: Lei Xue 
Signed-off-by: Dave Wysochanski 
Signed-off-by: David Howells 
Signed-off-by: Sasha Levin

fscache, cachefiles: remove redundant variable 'cache'

2018-12-17T08:38:34+00:00

[ Upstream commit 31ffa563833576bd49a8bf53120568312755e6e2 ]

Variable 'cache' is being assigned but is never used hence it is
redundant and can be removed.

Cleans up clang warning:
warning: variable 'cache' set but not used [-Wunused-but-set-variable]

Signed-off-by: Colin Ian King 
Signed-off-by: David Howells 
Signed-off-by: Sasha Levin

cachefiles: Fix page leak in cachefiles_read_backing_file while vmscan is active

2018-12-17T08:38:34+00:00

[ Upstream commit 9a24ce5b66f9c8190d63b15f4473600db4935f1f ]

[Description]

In a heavily loaded system where the system pagecache is nearing memory
limits and fscache is enabled, pages can be leaked by fscache while trying
read pages from cachefiles backend.  This can happen because two
applications can be reading same page from a single mount, two threads can
be trying to read the backing page at same time.  This results in one of
the threads finding that a page for the backing file or netfs file is
already in the radix tree.  During the error handling cachefiles does not
clean up the reference on backing page, leading to page leak.

[Fix]
The fix is straightforward, to decrement the reference when error is
encountered.

  [dhowells: Note that I've removed the clearance and put of newpage as
   they aren't attested in the commit message and don't appear to actually
   achieve anything since a new page is only allocated is newpage!=NULL and
   any residual new page is cleared before returning.]

[Testing]
I have tested the fix using following method for 12+ hrs.

1) mkdir -p /mnt/nfs ; mount -o vers=3,fsc :/export /mnt/nfs
2) create 10000 files of 2.8MB in a NFS mount.
3) start a thread to simulate heavy VM presssure
   (while true ; do echo 3 > /proc/sys/vm/drop_caches ; sleep 1 ; done)&
4) start multiple parallel reader for data set at same time
   find /mnt/nfs -type f | xargs -P 80 cat > /dev/null &
   find /mnt/nfs -type f | xargs -P 80 cat > /dev/null &
   find /mnt/nfs -type f | xargs -P 80 cat > /dev/null &
   ..
   ..
   find /mnt/nfs -type f | xargs -P 80 cat > /dev/null &
   find /mnt/nfs -type f | xargs -P 80 cat > /dev/null &
5) finally check using cat /proc/fs/fscache/stats | grep -i pages ;
   free -h , cat /proc/meminfo and page-types -r -b lru
   to ensure all pages are freed.

Reviewed-by: Daniel Axtens 
Signed-off-by: Shantanu Goel 
Signed-off-by: Kiran Kumar Modukuri 
[dja: forward ported to current upstream]
Signed-off-by: Daniel Axtens 
Signed-off-by: David Howells 
Signed-off-by: Sasha Levin

cachefiles: fix the race between cachefiles_bury_object() and rmdir(2)

2018-11-10T15:43:00+00:00

commit 169b803397499be85bdd1e3d07d6f5e3d4bd669e upstream.

the victim might've been rmdir'ed just before the lock_rename();
unlike the normal callers, we do not look the source up after the
parents are locked - we know it beforehand and just recheck that it's
still the child of what used to be its parent.  Unfortunately,
the check is too weak - we don't spot a dead directory since its
->d_parent is unchanged, dentry is positive, etc.  So we sail all
the way to ->rename(), with hosting filesystems _not_ expecting
to be asked renaming an rmdir'ed subdirectory.

The fix is easy, fortunately - the lock on parent is sufficient for
making IS_DEADDIR() on child safe.

Cc: stable@vger.kernel.org
Fixes: 9ae326a69004 (CacheFiles: A cache that backs onto a mounted filesystem)
Signed-off-by: Al Viro 
Signed-off-by: David Howells 
Signed-off-by: Greg Kroah-Hartman

cachefiles: Wait rather than BUG'ing on "Unexpected object collision"

2018-09-05T07:20:02+00:00

[ Upstream commit c2412ac45a8f8f1cd582723c1a139608694d410d ]

If we meet a conflicting object that is marked FSCACHE_OBJECT_IS_LIVE in
the active object tree, we have been emitting a BUG after logging
information about it and the new object.

Instead, we should wait for the CACHEFILES_OBJECT_ACTIVE flag to be cleared
on the old object (or return an error).  The ACTIVE flag should be cleared
after it has been removed from the active object tree.  A timeout of 60s is
used in the wait, so we shouldn't be able to get stuck there.

Fixes: 9ae326a69004 ("CacheFiles: A cache that backs onto a mounted filesystem")
Signed-off-by: Kiran Kumar Modukuri 
Signed-off-by: David Howells 
Signed-off-by: Sasha Levin 
Signed-off-by: Greg Kroah-Hartman

cachefiles: Fix refcounting bug in backing-file read monitoring

2018-09-05T07:20:02+00:00

[ Upstream commit 934140ab028713a61de8bca58c05332416d037d1 ]

cachefiles_read_waiter() has the right to access a 'monitor' object by
virtue of being called under the waitqueue lock for one of the pages in its
purview.  However, it has no ref on that monitor object or on the
associated operation.

What it is allowed to do is to move the monitor object to the operation's
to_do list, but once it drops the work_lock, it's actually no longer
permitted to access that object.  However, it is trying to enqueue the
retrieval operation for processing - but it can only do this via a pointer
in the monitor object, something it shouldn't be doing.

If it doesn't enqueue the operation, the operation may not get processed.
If the order is flipped so that the enqueue is first, then it's possible
for the work processor to look at the to_do list before the monitor is
enqueued upon it.

Fix this by getting a ref on the operation so that we can trust that it
will still be there once we've added the monitor to the to_do list and
dropped the work_lock.  The op can then be enqueued after the lock is
dropped.

The bug can manifest in one of a couple of ways.  The first manifestation
looks like:

 FS-Cache:
 FS-Cache: Assertion failed
 FS-Cache: 6 == 5 is false
 ------------[ cut here ]------------
 kernel BUG at fs/fscache/operation.c:494!
 RIP: 0010:fscache_put_operation+0x1e3/0x1f0
 ...
 fscache_op_work_func+0x26/0x50
 process_one_work+0x131/0x290
 worker_thread+0x45/0x360
 kthread+0xf8/0x130
 ? create_worker+0x190/0x190
 ? kthread_cancel_work_sync+0x10/0x10
 ret_from_fork+0x1f/0x30

This is due to the operation being in the DEAD state (6) rather than
INITIALISED, COMPLETE or CANCELLED (5) because it's already passed through
fscache_put_operation().

The bug can also manifest like the following:

 kernel BUG at fs/fscache/operation.c:69!
 ...
    [exception RIP: fscache_enqueue_operation+246]
 ...
 #7 [ffff883fff083c10] fscache_enqueue_operation at ffffffffa0b793c6
 #8 [ffff883fff083c28] cachefiles_read_waiter at ffffffffa0b15a48
 #9 [ffff883fff083c48] __wake_up_common at ffffffff810af028

I'm not entirely certain as to which is line 69 in Lei's kernel, so I'm not
entirely clear which assertion failed.

Fixes: 9ae326a69004 ("CacheFiles: A cache that backs onto a mounted filesystem")
Reported-by: Lei Xue 
Reported-by: Vegard Nossum 
Reported-by: Anthony DeRobertis 
Reported-by: NeilBrown 
Reported-by: Daniel Axtens 
Reported-by: Kiran Kumar Modukuri 
Signed-off-by: David Howells 
Reviewed-by: Daniel Axtens 
Signed-off-by: Sasha Levin 
Signed-off-by: Greg Kroah-Hartman

Merge branch 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs

2016-10-11T03:16:43+00:00

Pull more vfs updates from Al Viro:
 ">rename2() work from Miklos + current_time() from Deepa"

* 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs:
  fs: Replace current_fs_time() with current_time()
  fs: Replace CURRENT_TIME_SEC with current_time() for inode timestamps
  fs: Replace CURRENT_TIME with current_time() for inode timestamps
  fs: proc: Delete inode time initializations in proc_alloc_inode()
  vfs: Add current_time() api
  vfs: add note about i_op->rename changes to porting
  fs: rename "rename2" i_op to "rename"
  vfs: remove unused i_op->rename
  fs: make remaining filesystems use .rename2
  libfs: support RENAME_NOREPLACE in simple_rename()
  fs: support RENAME_NOREPLACE for local filesystems
  ncpfs: fix unused variable warning

Merge branch 'work.xattr' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs

2016-10-11T00:11:50+00:00

Pull vfs xattr updates from Al Viro:
 "xattr stuff from Andreas

  This completes the switch to xattr_handler ->get()/->set() from
  ->getxattr/->setxattr/->removexattr"

* 'work.xattr' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs:
  vfs: Remove {get,set,remove}xattr inode operations
  xattr: Stop calling {get,set,remove}xattr inode operations
  vfs: Check for the IOP_XATTR flag in listxattr
  xattr: Add __vfs_{get,set,remove}xattr helpers
  libfs: Use IOP_XATTR flag for empty directory handling
  vfs: Use IOP_XATTR flag for bad-inode handling
  vfs: Add IOP_XATTR inode operations flag
  vfs: Move xattr_resolve_name to the front of fs/xattr.c
  ecryptfs: Switch to generic xattr handlers
  sockfs: Get rid of getxattr iop
  sockfs: getxattr: Fail with -EOPNOTSUPP for invalid attribute names
  kernfs: Switch to generic xattr handlers
  hfs: Switch to generic xattr handlers
  jffs2: Remove jffs2_{get,set,remove}xattr macros
  xattr: Remove unnecessary NULL attribute name check

xattr: Add __vfs_{get,set,remove}xattr helpers

2016-10-08T00:10:44+00:00

Right now, various places in the kernel check for the existence of
getxattr, setxattr, and removexattr inode operations and directly call
those operations.  Switch to helper functions and test for the IOP_XATTR
flag instead.

Signed-off-by: Andreas Gruenbacher 
Acked-by: James Morris 
Signed-off-by: Al Viro

cachefiles: Fix attempt to read i_blocks after deleting file [ver #2]

2016-09-27T22:31:29+00:00

An NULL-pointer dereference happens in cachefiles_mark_object_inactive()
when it tries to read i_blocks so that it can tell the cachefilesd daemon
how much space it's making available.

The problem is that cachefiles_drop_object() calls
cachefiles_mark_object_inactive() after calling cachefiles_delete_object()
because the object being marked active staves off attempts to (re-)use the
file at that filename until after it has been deleted.  This means that
d_inode is NULL by the time we come to try to access it.

To fix the problem, have the caller of cachefiles_mark_object_inactive()
supply the number of blocks freed up.

Without this, the following oops may occur:

BUG: unable to handle kernel NULL pointer dereference at 0000000000000098
IP: [] cachefiles_mark_object_inactive+0x61/0xb0 [cachefiles]
...
CPU: 11 PID: 527 Comm: kworker/u64:4 Tainted: G          I    ------------   3.10.0-470.el7.x86_64 #1
Hardware name: Hewlett-Packard HP Z600 Workstation/0B54h, BIOS 786G4 v03.19 03/11/2011
Workqueue: fscache_object fscache_object_work_func [fscache]
task: ffff880035edaf10 ti: ffff8800b77c0000 task.ti: ffff8800b77c0000
RIP: 0010:[] cachefiles_mark_object_inactive+0x61/0xb0 [cachefiles]
RSP: 0018:ffff8800b77c3d70  EFLAGS: 00010246
RAX: 0000000000000000 RBX: ffff8800bf6cc400 RCX: 0000000000000034
RDX: 0000000000000000 RSI: ffff880090ffc710 RDI: ffff8800bf761ef8
RBP: ffff8800b77c3d88 R08: 2000000000000000 R09: 0090ffc710000000
R10: ff51005d2ff1c400 R11: 0000000000000000 R12: ffff880090ffc600
R13: ffff8800bf6cc520 R14: ffff8800bf6cc400 R15: ffff8800bf6cc498
FS:  0000000000000000(0000) GS:ffff8800bb8c0000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 000000008005003b
CR2: 0000000000000098 CR3: 00000000019ba000 CR4: 00000000000007e0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000400
Stack:
 ffff880090ffc600 ffff8800bf6cc400 ffff8800867df140 ffff8800b77c3db0
 ffffffffa06c48cb ffff880090ffc600 ffff880090ffc180 ffff880090ffc658
 ffff8800b77c3df0 ffffffffa085d846 ffff8800a96b8150 ffff880090ffc600
Call Trace:
 [] cachefiles_drop_object+0x6b/0xf0 [cachefiles]
 [] fscache_drop_object+0xd6/0x1e0 [fscache]
 [] fscache_object_work_func+0xa5/0x200 [fscache]
 [] process_one_work+0x17b/0x470
 [] worker_thread+0x126/0x410
 [] ? rescuer_thread+0x460/0x460
 [] kthread+0xcf/0xe0
 [] ? kthread_create_on_node+0x140/0x140
 [] ret_from_fork+0x58/0x90
 [] ? kthread_create_on_node+0x140/0x140

The oopsing code shows:

	callq  0xffffffff810af6a0 
	mov    0xf8(%r12),%rax
	mov    0x30(%rax),%rax
	mov    0x98(%rax),%rax   <---- oops here
	lock add %rax,0x130(%rbx)

where this is:

	d_backing_inode(object->dentry)->i_blocks

Fixes: a5b3a80b899bda0f456f1246c4c5a1191ea01519 (CacheFiles: Provide read-and-reset release counters for cachefilesd)
Reported-by: Jianhong Yin 
Signed-off-by: David Howells 
Reviewed-by: Jeff Layton 
Reviewed-by: Steve Dickson 
cc: stable@vger.kernel.org
Signed-off-by: Al Viro