[PATCH 0/2] afs: Fixes

[PATCH 0/2] afs: Fixes

[David Howells]

Hi Linus,

Here are two fix patches for the AFS filesystem:

 (1) Fix the refcounting on permit caching.

 (2) AFS inode (afs_vnode) fields need resetting after allocation because
     they're only initialised when slab pages are obtained from the page
     allocator.

The patches can be found here also:

	http://git.kernel.org/cgit/linux/kernel/git/dhowells/linux-fs.git/log/?h=afs-fixes

tagged thusly:

	afs-fixes-20171201

David
---
David Howells (2):
      afs: Fix permit refcounting
      afs: Properly reset afs_vnode (inode) fields


 fs/afs/internal.h |    5 ++++-
 fs/afs/security.c |   18 ++++++++++--------
 fs/afs/super.c    |   14 +++++++++++++-
 3 files changed, 27 insertions(+), 10 deletions(-)

[PATCH 1/2] afs: Fix permit refcounting

[David Howells]

Fix four refcount bugs in afs_cache_permit():

 (1) When checking the result of the kzalloc(), we can't just return, but
     must put 'permits'.

 (2) We shouldn't put permits immediately after hashing a new permit as we
     need to keep the pointer stable so that we can check to see if
     vnode->permit_cache has changed before we decide whether to assign to
     it.

 (3) 'permits' is being put twice.

 (4) We need to put either the replacement or the thing replaced after the
     assignment to vnode->permit_cache.

Without this, lots of the following are seen:

  Kernel BUG at ffffffffa039857b [verbose debug info unavailable]
  ------------[ cut here ]------------
  Kernel BUG at ffffffffa039858a [verbose debug info unavailable]
  ------------[ cut here ]------------

The addresses are in the .text..refcount section of the kafs.ko module.
Following the relocation records for the __ex_table section shows one to be
due to the decrement in afs_put_permits() and the other to be key_get() in
afs_cache_permit().

Occasionally, the following is seen:

  refcount_t overflow at afs_cache_permit+0x57d/0x5c0 [kafs] in cc1[562], uid/euid: 0/0
  WARNING: CPU: 0 PID: 562 at kernel/panic.c:657 refcount_error_report+0x9c/0xac
  ...

Reported-by: Marc Dionne <marc.dionne@auristor.com>
Signed-off-by: David Howells <dhowells@redhat.com>
Tested-by: Marc Dionne <marc.dionne@auristor.com>
---

 fs/afs/security.c |   18 ++++++++++--------
 1 file changed, 10 insertions(+), 8 deletions(-)

diff --git a/fs/afs/security.c b/fs/afs/security.c
index 2b00097101b3..b88b7d45fdaa 100644
--- a/fs/afs/security.c
+++ b/fs/afs/security.c
@@ -120,7 +120,7 @@ static void afs_hash_permits(struct afs_permits *permits)
 void afs_cache_permit(struct afs_vnode *vnode, struct key *key,
 		      unsigned int cb_break)
 {
-	struct afs_permits *permits, *xpermits, *replacement, *new = NULL;
+	struct afs_permits *permits, *xpermits, *replacement, *zap, *new = NULL;
 	afs_access_t caller_access = READ_ONCE(vnode->status.caller_access);
 	size_t size = 0;
 	bool changed = false;
@@ -204,7 +204,7 @@ void afs_cache_permit(struct afs_vnode *vnode, struct key *key,
 	new = kzalloc(sizeof(struct afs_permits) +
 		      sizeof(struct afs_permit) * size, GFP_NOFS);
 	if (!new)
-		return;
+		goto out_put;
 
 	refcount_set(&new->usage, 1);
 	new->nr_permits = size;
@@ -229,8 +229,6 @@ void afs_cache_permit(struct afs_vnode *vnode, struct key *key,
 
 	afs_hash_permits(new);
 
-	afs_put_permits(permits);
-
 	/* Now see if the permit list we want is actually already available */
 	spin_lock(&afs_permits_lock);
 
@@ -262,11 +260,15 @@ void afs_cache_permit(struct afs_vnode *vnode, struct key *key,
 	kfree(new);
 
 	spin_lock(&vnode->lock);
-	if (cb_break != (vnode->cb_break + vnode->cb_interest->server->cb_s_break) ||
-	    permits != rcu_access_pointer(vnode->permit_cache))
-		goto someone_else_changed_it_unlock;
-	rcu_assign_pointer(vnode->permit_cache, replacement);
+	zap = rcu_access_pointer(vnode->permit_cache);
+	if (cb_break == (vnode->cb_break + vnode->cb_interest->server->cb_s_break) &&
+	    zap == permits)
+		rcu_assign_pointer(vnode->permit_cache, replacement);
+	else
+		zap = replacement;
 	spin_unlock(&vnode->lock);
+	afs_put_permits(zap);
+out_put:
 	afs_put_permits(permits);
 	return;
 

[PATCH 2/2] afs: Properly reset afs_vnode (inode) fields

[David Howells]

When an AFS inode is allocated by afs_alloc_inode(), the allocated
afs_vnode struct isn't necessarily reset from the last time it was used as
an inode because the slab constructor is only invoked once when the memory
is obtained from the page allocator.

This means that information can leak from one inode to the next because
we're not calling kmem_cache_zalloc().  Some of the information isn't
reset, in particular the permit cache pointer.

Bring the clearances up to date.

Signed-off-by: David Howells <dhowells@redhat.com>
Tested-by: Marc Dionne <marc.dionne@auristor.com>
---

 fs/afs/internal.h |    5 ++++-
 fs/afs/super.c    |   14 +++++++++++++-
 2 files changed, 17 insertions(+), 2 deletions(-)

diff --git a/fs/afs/internal.h b/fs/afs/internal.h
index e03910cebdd4..804d1f905622 100644
--- a/fs/afs/internal.h
+++ b/fs/afs/internal.h
@@ -441,7 +441,10 @@ enum afs_lock_state {
 };
 
 /*
- * AFS inode private data
+ * AFS inode private data.
+ *
+ * Note that afs_alloc_inode() *must* reset anything that could incorrectly
+ * leak from one inode to another.
  */
 struct afs_vnode {
 	struct inode		vfs_inode;	/* the VFS's inode record */
diff --git a/fs/afs/super.c b/fs/afs/super.c
index d3f97da61bdf..1037dd41a622 100644
--- a/fs/afs/super.c
+++ b/fs/afs/super.c
@@ -536,7 +536,9 @@ static void afs_kill_super(struct super_block *sb)
 }
 
 /*
- * initialise an inode cache slab element prior to any use
+ * Initialise an inode cache slab element prior to any use.  Note that
+ * afs_alloc_inode() *must* reset anything that could incorrectly leak from one
+ * inode to another.
  */
 static void afs_i_init_once(void *_vnode)
 {
@@ -568,11 +570,21 @@ static struct inode *afs_alloc_inode(struct super_block *sb)
 
 	atomic_inc(&afs_count_active_inodes);
 
+	/* Reset anything that shouldn't leak from one inode to the next. */
 	memset(&vnode->fid, 0, sizeof(vnode->fid));
 	memset(&vnode->status, 0, sizeof(vnode->status));
 
 	vnode->volume		= NULL;
+	vnode->lock_key		= NULL;
+	vnode->permit_cache	= NULL;
+	vnode->cb_interest	= NULL;
+#ifdef CONFIG_AFS_FSCACHE
+	vnode->cache		= NULL;
+#endif
+
 	vnode->flags		= 1 << AFS_VNODE_UNSET;
+	vnode->cb_type		= 0;
+	vnode->lock_state	= AFS_VNODE_LOCK_NONE;
 
 	_leave(" = %p", &vnode->vfs_inode);
 	return &vnode->vfs_inode;