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Al Viro 9ea0a46ca2 fix mntput/mntput race 
mntput_no_expire() does the calculation of total refcount under mount_lock;
unfortunately, the decrement (as well as all increments) are done outside
of it, leading to false positives in the "are we dropping the last reference"
test.  Consider the following situation:
	* mnt is a lazy-umounted mount, kept alive by two opened files.  One
of those files gets closed.  Total refcount of mnt is 2.  On CPU 42
mntput(mnt) (called from __fput()) drops one reference, decrementing component
	* After it has looked at component #0, the process on CPU 0 does
mntget(), incrementing component #0, gets preempted and gets to run again -
on CPU 69.  There it does mntput(), which drops the reference (component #69)
and proceeds to spin on mount_lock.
	* On CPU 42 our first mntput() finishes counting.  It observes the
decrement of component #69, but not the increment of component #0.  As the
result, the total it gets is not 1 as it should've been - it's 0.  At which
point we decide that vfsmount needs to be killed and proceed to free it and
shut the filesystem down.  However, there's still another opened file
on that filesystem, with reference to (now freed) vfsmount, etc. and we are
screwed.

It's not a wide race, but it can be reproduced with artificial slowdown of
the mnt_get_count() loop, and it should be easier to hit on SMP KVM setups.

Fix consists of moving the refcount decrement under mount_lock; the tricky
part is that we want (and can) keep the fast case (i.e. mount that still
has non-NULL ->mnt_ns) entirely out of mount_lock.  All places that zero
mnt->mnt_ns are dropping some reference to mnt and they call synchronize_rcu()
before that mntput().  IOW, if mntput() observes (under rcu_read_lock())
a non-NULL ->mnt_ns, it is guaranteed that there is another reference yet to
be dropped.

Reported-by: Jann Horn <jannh@google.com>
Tested-by: Jann Horn <jannh@google.com>
Fixes: 48a066e72d ("RCU'd vsfmounts")
Cc: stable@vger.kernel.org
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
2018-08-09 17:21:17 -04:00
..
9p treewide: kmalloc() -> kmalloc_array() 2018-06-12 16:19:22 -07:00
adfs vfs/y2038: inode timestamps conversion to timespec64 2018-06-15 07:31:07 +09:00
affs affs: fix potential memory leak when parsing option 'prefix' 2018-05-28 12:36:41 +02:00
afs Merge branch 'afs-proc' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs 2018-06-16 16:32:04 +09:00
autofs autofs: Fix typo s/thenew new/the new/ in AUTOFS4_FS description 2018-06-12 12:31:19 -07:00
befs fix a series of Documentation/ broken file name references 2018-06-15 18:10:01 -03:00
bfs bfs_add_entry: pass name/len as qstr pointer 2018-05-22 14:27:50 -04:00
btrfs vfs/y2038: inode timestamps conversion to timespec64 2018-06-15 07:31:07 +09:00
cachefiles Merge branch 'hch.procfs' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs 2018-06-04 10:00:01 -07:00
ceph vfs/y2038: inode timestamps conversion to timespec64 2018-06-15 07:31:07 +09:00
cifs vfs/y2038: inode timestamps conversion to timespec64 2018-06-15 07:31:07 +09:00
coda vfs: change inode times to use struct timespec64 2018-06-05 16:57:31 -07:00
configfs vfs: change inode times to use struct timespec64 2018-06-05 16:57:31 -07:00
cramfs vfs/y2038: inode timestamps conversion to timespec64 2018-06-15 07:31:07 +09:00
crypto f2fs-for-4.18-rc1 2018-06-11 10:16:13 -07:00
debugfs Revert "debugfs: inode: debugfs_create_dir uses mode permission from parent" 2018-06-12 20:52:16 -07:00
devpts
dlm treewide: Use array_size() in vmalloc() 2018-06-12 16:19:22 -07:00
ecryptfs Merge branch 'fixes' of https://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs into aio-base 2018-05-26 09:16:25 +02:00
efivarfs
efs
exofs exofs: avoid VLA in structures 2018-06-15 07:55:24 +09:00
exportfs ovl: do not try to reconnect a disconnected origin dentry 2018-04-12 12:04:49 +02:00
ext2 treewide: kmalloc() -> kmalloc_array() 2018-06-12 16:19:22 -07:00
ext4 vfs/y2038: inode timestamps conversion to timespec64 2018-06-15 07:31:07 +09:00
f2fs vfs/y2038: inode timestamps conversion to timespec64 2018-06-15 07:31:07 +09:00
fat Merge branch 'akpm' (patches from Andrew) 2018-06-15 08:51:42 +09:00
freevxfs freevxfs_lookup(): use d_splice_alias() 2018-05-22 14:27:51 -04:00
fscache proc: introduce proc_create_single{,_data} 2018-05-16 07:23:35 +02:00
fuse vfs/y2038: inode timestamps conversion to timespec64 2018-06-15 07:31:07 +09:00
gfs2 vfs/y2038: inode timestamps conversion to timespec64 2018-06-15 07:31:07 +09:00
hfs vfs/y2038: inode timestamps conversion to timespec64 2018-06-15 07:31:07 +09:00
hfsplus vfs/y2038: inode timestamps conversion to timespec64 2018-06-15 07:31:07 +09:00
hostfs vfs: change inode times to use struct timespec64 2018-06-05 16:57:31 -07:00
hpfs treewide: kmalloc() -> kmalloc_array() 2018-06-12 16:19:22 -07:00
hugetlbfs
isofs isofs: fix potential memory leak in mount option parsing 2018-04-16 09:47:41 +02:00
jbd2 treewide: kmalloc() -> kmalloc_array() 2018-06-12 16:19:22 -07:00
jffs2 vfs/y2038: inode timestamps conversion to timespec64 2018-06-15 07:31:07 +09:00
jfs treewide: kmalloc() -> kmalloc_array() 2018-06-12 16:19:22 -07:00
kernfs vfs/y2038: inode timestamps conversion to timespec64 2018-06-15 07:31:07 +09:00
lockd
minix minix_lookup: use d_splice_alias() 2018-05-22 14:27:52 -04:00
nfs vfs/y2038: inode timestamps conversion to timespec64 2018-06-15 07:31:07 +09:00
nfs_common
nfsd vfs/y2038: inode timestamps conversion to timespec64 2018-06-15 07:31:07 +09:00
nilfs2 do d_instantiate/unlock_new_inode combinations safely 2018-05-11 15:36:37 -04:00
nls
notify fsnotify: add fsnotify_add_inode_mark() wrappers 2018-05-18 14:58:22 +02:00
ntfs vfs/y2038: inode timestamps conversion to timespec64 2018-06-15 07:31:07 +09:00
ocfs2 vfs/y2038: inode timestamps conversion to timespec64 2018-06-15 07:31:07 +09:00
omfs omfs_lookup(): report IO errors, use d_splice_alias() 2018-05-22 14:27:58 -04:00
openpromfs openpromfs: switch to d_splice_alias() 2018-05-22 14:27:57 -04:00
orangefs Solve a series of broken links for files under Documentation: 2018-06-17 05:25:18 +09:00
overlayfs vfs/y2038: inode timestamps conversion to timespec64 2018-06-15 07:31:07 +09:00
proc proc: add proc_seq_release 2018-06-27 20:44:38 -04:00
pstore pstore: Remove bogus format string definition 2018-06-14 14:57:24 +02:00
qnx4 qnx4_lookup: use d_splice_alias() 2018-05-22 14:27:52 -04:00
qnx6 qnx6_lookup: switch to d_splice_alias() 2018-05-22 14:27:54 -04:00
quota fs: quota: Replace GFP_ATOMIC with GFP_KERNEL in dquot_init 2018-04-09 17:48:54 +02:00
ramfs
reiserfs vfs/y2038: inode timestamps conversion to timespec64 2018-06-15 07:31:07 +09:00
romfs romfs_lookup: switch to d_splice_alias() 2018-05-22 14:27:55 -04:00
squashfs
sysfs unfuck sysfs_mount() 2018-05-21 14:30:09 -04:00
sysv sysv_lookup: use d_splice_alias() 2018-05-22 14:27:53 -04:00
tracefs
ubifs vfs/y2038: inode timestamps conversion to timespec64 2018-06-15 07:31:07 +09:00
udf vfs/y2038: inode timestamps conversion to timespec64 2018-06-15 07:31:07 +09:00
ufs treewide: kmalloc() -> kmalloc_array() 2018-06-12 16:19:22 -07:00
xfs vfs/y2038: inode timestamps conversion to timespec64 2018-06-15 07:31:07 +09:00
aio.c aio: don't expose __aio_sigset in uapi 2018-07-17 23:26:58 -04:00
anon_inodes.c
attr.c vfs/y2038: inode timestamps conversion to timespec64 2018-06-15 07:31:07 +09:00
bad_inode.c vfs: change inode times to use struct timespec64 2018-06-05 16:57:31 -07:00
binfmt_aout.c exec: introduce finalize_exec() before start_thread() 2018-04-11 10:28:37 -07:00
binfmt_elf.c coredump: fix spam with zero VMA process 2018-06-15 07:55:24 +09:00
binfmt_elf_fdpic.c treewide: kmalloc() -> kmalloc_array() 2018-06-12 16:19:22 -07:00
binfmt_em86.c
binfmt_flat.c exec: introduce finalize_exec() before start_thread() 2018-04-11 10:28:37 -07:00
binfmt_misc.c docs: Fix more broken references 2018-06-15 18:11:26 -03:00
binfmt_script.c
block_dev.c treewide: kmalloc() -> kmalloc_array() 2018-06-12 16:19:22 -07:00
buffer.c fs: move page_cache_seek_hole_data to iomap.c 2018-06-01 18:37:33 -07:00
char_dev.c
compat.c ncpfs: remove compat functionality 2018-06-05 19:23:26 +02:00
compat_binfmt_elf.c
compat_ioctl.c autofs: clean up includes 2018-06-07 17:34:40 -07:00
coredump.c
d_path.c
dax.c libnvdimm for 4.18 2018-06-08 17:21:52 -07:00
dcache.c root dentries need RCU-delayed freeing 2018-08-06 09:13:32 -04:00
dcookies.c
direct-io.c block: consistently use GFP_NOIO instead of __GFP_NORECLAIM 2018-05-14 08:55:18 -06:00
drop_caches.c
eventfd.c eventfd: only return events requested in poll_mask() 2018-06-14 20:07:38 -04:00
eventpoll.c eventpoll: switch to ->poll_mask 2018-06-14 20:09:28 -04:00
exec.c Merge branch 'core-rseq-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip 2018-06-10 10:17:09 -07:00
fcntl.c mm: restructure memfd code 2018-06-07 17:34:35 -07:00
fhandle.c
file.c
file_table.c
filesystems.c proc: introduce proc_create_single{,_data} 2018-05-16 07:23:35 +02:00
fs-writeback.c bdi: Fix oops in wb_workfn() 2018-05-03 16:11:37 -06:00
fs_pin.c
fs_struct.c
inode.c vfs/y2038: inode timestamps conversion to timespec64 2018-06-15 07:31:07 +09:00
internal.h drm_mode_create_lease_ioctl(): fix open-coded filp_clone_open() 2018-07-10 23:29:03 -04:00
ioctl.c fs: Allow CAP_SYS_ADMIN in s_user_ns to freeze and thaw filesystems 2018-05-24 12:04:28 -05:00
iomap.c Changes since last update: 2018-06-12 15:49:00 -07:00
Kconfig autofs: remove left-over autofs4 stubs 2018-06-11 08:22:34 -07:00
Kconfig.binfmt docs: Fix more broken references 2018-06-15 18:11:26 -03:00
libfs.c
locks.c vfs/y2038: inode timestamps conversion to timespec64 2018-06-15 07:31:07 +09:00
Makefile autofs: remove left-over autofs4 stubs 2018-06-11 08:22:34 -07:00
mbcache.c treewide: kmalloc() -> kmalloc_array() 2018-06-12 16:19:22 -07:00
mount.h
mpage.c
namei.c Merge branch 'afs-proc' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs 2018-06-16 16:32:04 +09:00
namespace.c fix mntput/mntput race 2018-08-09 17:21:17 -04:00
no-block.c
nsfs.c
open.c Revert "fs: fold open_check_o_direct into do_dentry_open" 2018-06-03 10:58:23 -07:00
pipe.c pipe: convert to ->poll_mask 2018-05-26 09:16:44 +02:00
pnode.c
pnode.h
posix_acl.c
proc_namespace.c
read_write.c treewide: kmalloc() -> kmalloc_array() 2018-06-12 16:19:22 -07:00
readdir.c
select.c treewide: kmalloc() -> kmalloc_array() 2018-06-12 16:19:22 -07:00
seq_file.c proc: fix smaps and meminfo alignment 2018-05-25 18:12:11 -07:00
signalfd.c Merge branch 'work.compat' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs 2018-06-16 16:21:50 +09:00
splice.c Merge branch 'work.compat' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs 2018-06-16 16:21:50 +09:00
stack.c
stat.c
statfs.c
super.c Merge branch 'work.misc' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs 2018-06-04 10:14:28 -07:00
sync.c
timerfd.c timerfd: convert to ->poll_mask 2018-05-26 09:16:44 +02:00
userfaultfd.c userfaultfd: prevent non-cooperative events vs mcopy_atomic races 2018-06-07 17:34:38 -07:00
utimes.c
xattr.c vfs: delete unnecessary assignment in vfs_listxattr 2018-05-29 13:22:41 -04:00