--- /dev/null
+From 119e1ef80ecfe0d1deb6378d4ab41f5b71519de1 Mon Sep 17 00:00:00 2001
+From: Al Viro <viro@zeniv.linux.org.uk>
+Date: Thu, 9 Aug 2018 17:51:32 -0400
+Subject: fix __legitimize_mnt()/mntput() race
+
+From: Al Viro <viro@zeniv.linux.org.uk>
+
+commit 119e1ef80ecfe0d1deb6378d4ab41f5b71519de1 upstream.
+
+__legitimize_mnt() has two problems - one is that in case of success
+the check of mount_lock is not ordered wrt preceding increment of
+refcount, making it possible to have successful __legitimize_mnt()
+on one CPU just before the otherwise final mntpu() on another,
+with __legitimize_mnt() not seeing mntput() taking the lock and
+mntput() not seeing the increment done by __legitimize_mnt().
+Solved by a pair of barriers.
+
+Another is that failure of __legitimize_mnt() on the second
+read_seqretry() leaves us with reference that'll need to be
+dropped by caller; however, if that races with final mntput()
+we can end up with caller dropping rcu_read_lock() and doing
+mntput() to release that reference - with the first mntput()
+having freed the damn thing just as rcu_read_lock() had been
+dropped. Solution: in "do mntput() yourself" failure case
+grab mount_lock, check if MNT_DOOMED has been set by racing
+final mntput() that has missed our increment and if it has -
+undo the increment and treat that as "failure, caller doesn't
+need to drop anything" case.
+
+It's not easy to hit - the final mntput() has to come right
+after the first read_seqretry() in __legitimize_mnt() *and*
+manage to miss the increment done by __legitimize_mnt() before
+the second read_seqretry() in there. The things that are almost
+impossible to hit on bare hardware are not impossible on SMP
+KVM, though...
+
+Reported-by: Oleg Nesterov <oleg@redhat.com>
+Fixes: 48a066e72d97 ("RCU'd vsfmounts")
+Cc: stable@vger.kernel.org
+Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
+Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
+
+---
+ fs/namespace.c | 14 ++++++++++++++
+ 1 file changed, 14 insertions(+)
+
+--- a/fs/namespace.c
++++ b/fs/namespace.c
+@@ -603,12 +603,21 @@ int __legitimize_mnt(struct vfsmount *ba
+ return 0;
+ mnt = real_mount(bastard);
+ mnt_add_count(mnt, 1);
++ smp_mb(); // see mntput_no_expire()
+ if (likely(!read_seqretry(&mount_lock, seq)))
+ return 0;
+ if (bastard->mnt_flags & MNT_SYNC_UMOUNT) {
+ mnt_add_count(mnt, -1);
+ return 1;
+ }
++ lock_mount_hash();
++ if (unlikely(bastard->mnt_flags & MNT_DOOMED)) {
++ mnt_add_count(mnt, -1);
++ unlock_mount_hash();
++ return 1;
++ }
++ unlock_mount_hash();
++ /* caller will mntput() */
+ return -1;
+ }
+
+@@ -1154,6 +1163,11 @@ static void mntput_no_expire(struct moun
+ return;
+ }
+ lock_mount_hash();
++ /*
++ * make sure that if __legitimize_mnt() has not seen us grab
++ * mount_lock, we'll see their refcount increment here.
++ */
++ smp_mb();
+ mnt_add_count(mnt, -1);
+ if (mnt_get_count(mnt)) {
+ rcu_read_unlock();
--- /dev/null
+From 9ea0a46ca2c318fcc449c1e6b62a7230a17888f1 Mon Sep 17 00:00:00 2001
+From: Al Viro <viro@zeniv.linux.org.uk>
+Date: Thu, 9 Aug 2018 17:21:17 -0400
+Subject: fix mntput/mntput race
+
+From: Al Viro <viro@zeniv.linux.org.uk>
+
+commit 9ea0a46ca2c318fcc449c1e6b62a7230a17888f1 upstream.
+
+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: 48a066e72d97 ("RCU'd vsfmounts")
+Cc: stable@vger.kernel.org
+Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
+Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
+
+---
+ fs/namespace.c | 14 ++++++++++++--
+ 1 file changed, 12 insertions(+), 2 deletions(-)
+
+--- a/fs/namespace.c
++++ b/fs/namespace.c
+@@ -1139,12 +1139,22 @@ static DECLARE_DELAYED_WORK(delayed_mntp
+ static void mntput_no_expire(struct mount *mnt)
+ {
+ rcu_read_lock();
+- mnt_add_count(mnt, -1);
+- if (likely(mnt->mnt_ns)) { /* shouldn't be the last one */
++ if (likely(READ_ONCE(mnt->mnt_ns))) {
++ /*
++ * Since we don't do lock_mount_hash() here,
++ * ->mnt_ns can change under us. However, if it's
++ * non-NULL, then there's a reference that won't
++ * be dropped until after an RCU delay done after
++ * turning ->mnt_ns NULL. So if we observe it
++ * non-NULL under rcu_read_lock(), the reference
++ * we are dropping is not the final one.
++ */
++ mnt_add_count(mnt, -1);
+ rcu_read_unlock();
+ return;
+ }
+ lock_mount_hash();
++ mnt_add_count(mnt, -1);
+ if (mnt_get_count(mnt)) {
+ rcu_read_unlock();
+ unlock_mount_hash();
--- /dev/null
+From 4c0d7cd5c8416b1ef41534d19163cb07ffaa03ab Mon Sep 17 00:00:00 2001
+From: Al Viro <viro@zeniv.linux.org.uk>
+Date: Thu, 9 Aug 2018 10:15:54 -0400
+Subject: make sure that __dentry_kill() always invalidates d_seq, unhashed or not
+
+From: Al Viro <viro@zeniv.linux.org.uk>
+
+commit 4c0d7cd5c8416b1ef41534d19163cb07ffaa03ab upstream.
+
+RCU pathwalk relies upon the assumption that anything that changes
+->d_inode of a dentry will invalidate its ->d_seq. That's almost
+true - the one exception is that the final dput() of already unhashed
+dentry does *not* touch ->d_seq at all. Unhashing does, though,
+so for anything we'd found by RCU dcache lookup we are fine.
+Unfortunately, we can *start* with an unhashed dentry or jump into
+it.
+
+We could try and be careful in the (few) places where that could
+happen. Or we could just make the final dput() invalidate the damn
+thing, unhashed or not. The latter is much simpler and easier to
+backport, so let's do it that way.
+
+Reported-by: "Dae R. Jeong" <threeearcat@gmail.com>
+Cc: stable@vger.kernel.org
+Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
+Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
+
+---
+ fs/dcache.c | 7 ++-----
+ 1 file changed, 2 insertions(+), 5 deletions(-)
+
+--- a/fs/dcache.c
++++ b/fs/dcache.c
+@@ -352,14 +352,11 @@ static void dentry_unlink_inode(struct d
+ __releases(dentry->d_inode->i_lock)
+ {
+ struct inode *inode = dentry->d_inode;
+- bool hashed = !d_unhashed(dentry);
+
+- if (hashed)
+- raw_write_seqcount_begin(&dentry->d_seq);
++ raw_write_seqcount_begin(&dentry->d_seq);
+ __d_clear_type_and_inode(dentry);
+ hlist_del_init(&dentry->d_u.d_alias);
+- if (hashed)
+- raw_write_seqcount_end(&dentry->d_seq);
++ raw_write_seqcount_end(&dentry->d_seq);
+ spin_unlock(&dentry->d_lock);
+ spin_unlock(&inode->i_lock);
+ if (!inode->i_nlink)
--- /dev/null
+From 90bad5e05bcdb0308cfa3d3a60f5c0b9c8e2efb3 Mon Sep 17 00:00:00 2001
+From: Al Viro <viro@zeniv.linux.org.uk>
+Date: Mon, 6 Aug 2018 09:03:58 -0400
+Subject: root dentries need RCU-delayed freeing
+
+From: Al Viro <viro@zeniv.linux.org.uk>
+
+commit 90bad5e05bcdb0308cfa3d3a60f5c0b9c8e2efb3 upstream.
+
+Since mountpoint crossing can happen without leaving lazy mode,
+root dentries do need the same protection against having their
+memory freed without RCU delay as everything else in the tree.
+
+It's partially hidden by RCU delay between detaching from the
+mount tree and dropping the vfsmount reference, but the starting
+point of pathwalk can be on an already detached mount, in which
+case umount-caused RCU delay has already passed by the time the
+lazy pathwalk grabs rcu_read_lock(). If the starting point
+happens to be at the root of that vfsmount *and* that vfsmount
+covers the entire filesystem, we get trouble.
+
+Fixes: 48a066e72d97 ("RCU'd vsfmounts")
+Cc: stable@vger.kernel.org
+Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
+Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
+
+---
+ fs/dcache.c | 6 ++++--
+ 1 file changed, 4 insertions(+), 2 deletions(-)
+
+--- a/fs/dcache.c
++++ b/fs/dcache.c
+@@ -1914,10 +1914,12 @@ struct dentry *d_make_root(struct inode
+
+ if (root_inode) {
+ res = __d_alloc(root_inode->i_sb, NULL);
+- if (res)
++ if (res) {
++ res->d_flags |= DCACHE_RCUACCESS;
+ d_instantiate(res, root_inode);
+- else
++ } else {
+ iput(root_inode);
++ }
+ }
+ return res;
+ }
acpi-lpss-add-missing-prv_offset-setting-for-byt-cht-pwm-devices.patch
scsi-sr-avoid-that-opening-a-cd-rom-hangs-with-runtime-power-management-enabled.patch
init-rename-and-re-order-boot_cpu_state_init.patch
+root-dentries-need-rcu-delayed-freeing.patch
+make-sure-that-__dentry_kill-always-invalidates-d_seq-unhashed-or-not.patch
+fix-mntput-mntput-race.patch
+fix-__legitimize_mnt-mntput-race.patch
projects / thirdparty / kernel / stable-queue.git / commitdiff
