[PATCH 24/25] afs: Fix callback handling [ver #2]

[David Howells]

In some circumstances, the callback interest pointer is NULL, so in such a
case we can't dereference it when checking to see if the callback is
broken.  This causes an oops in some circumstances.

Fix this by replacing the function that worked out the aggregate break
counter with one that actually does the comparison, and then make that
return true (ie. broken) if there is no callback interest as yet (ie. the
pointer is NULL).

Fixes: 68251f0a6818 ("afs: Fix whole-volume callback handling")
Signed-off-by: David Howells <dhowells@xxxxxxxxxx>
---

 fs/afs/fsclient.c  |    2 +-
 fs/afs/internal.h  |    9 ++++++---
 fs/afs/security.c  |    7 ++++---
 fs/afs/yfsclient.c |    2 +-
 4 files changed, 12 insertions(+), 8 deletions(-)

diff --git a/fs/afs/fsclient.c b/fs/afs/fsclient.c
index 3975969719de..7c75a1813321 100644
--- a/fs/afs/fsclient.c
+++ b/fs/afs/fsclient.c
@@ -269,7 +269,7 @@ static void xdr_decode_AFSCallBack(struct afs_call *call,
 
 	write_seqlock(&vnode->cb_lock);
 
-	if (call->cb_break == afs_cb_break_sum(vnode, cbi)) {
+	if (!afs_cb_is_broken(call->cb_break, vnode, cbi)) {
 		vnode->cb_version	= ntohl(*bp++);
 		cb_expiry		= ntohl(*bp++);
 		vnode->cb_type		= ntohl(*bp++);
diff --git a/fs/afs/internal.h b/fs/afs/internal.h
index e5b596bd8acf..b60d15212975 100644
--- a/fs/afs/internal.h
+++ b/fs/afs/internal.h
@@ -776,10 +776,13 @@ static inline unsigned int afs_calc_vnode_cb_break(struct afs_vnode *vnode)
 	return vnode->cb_break + vnode->cb_s_break + vnode->cb_v_break;
 }
 
-static inline unsigned int afs_cb_break_sum(struct afs_vnode *vnode,
-					    struct afs_cb_interest *cbi)
+static inline bool afs_cb_is_broken(unsigned int cb_break,
+				    const struct afs_vnode *vnode,
+				    const struct afs_cb_interest *cbi)
 {
-	return vnode->cb_break + cbi->server->cb_s_break + vnode->volume->cb_v_break;
+	return !cbi || cb_break != (vnode->cb_break +
+				    cbi->server->cb_s_break +
+				    vnode->volume->cb_v_break);
 }
 
 /*
diff --git a/fs/afs/security.c b/fs/afs/security.c
index d1ae53fd3739..5f58a9a17e69 100644
--- a/fs/afs/security.c
+++ b/fs/afs/security.c
@@ -147,7 +147,8 @@ void afs_cache_permit(struct afs_vnode *vnode, struct key *key,
 					break;
 				}
 
-				if (cb_break != afs_cb_break_sum(vnode, vnode->cb_interest)) {
+				if (afs_cb_is_broken(cb_break, vnode,
+						     vnode->cb_interest)) {
 					changed = true;
 					break;
 				}
@@ -177,7 +178,7 @@ void afs_cache_permit(struct afs_vnode *vnode, struct key *key,
 		}
 	}
 
-	if (cb_break != afs_cb_break_sum(vnode, vnode->cb_interest))
+	if (afs_cb_is_broken(cb_break, vnode, vnode->cb_interest))
 		goto someone_else_changed_it;
 
 	/* We need a ref on any permits list we want to copy as we'll have to
@@ -256,7 +257,7 @@ void afs_cache_permit(struct afs_vnode *vnode, struct key *key,
 
 	spin_lock(&vnode->lock);
 	zap = rcu_access_pointer(vnode->permit_cache);
-	if (cb_break == afs_cb_break_sum(vnode, vnode->cb_interest) &&
+	if (!afs_cb_is_broken(cb_break, vnode, vnode->cb_interest) &&
 	    zap == permits)
 		rcu_assign_pointer(vnode->permit_cache, replacement);
 	else
diff --git a/fs/afs/yfsclient.c b/fs/afs/yfsclient.c
index d5e3f0095040..12658c1363ae 100644
--- a/fs/afs/yfsclient.c
+++ b/fs/afs/yfsclient.c
@@ -324,7 +324,7 @@ static void xdr_decode_YFSCallBack(struct afs_call *call,
 
 	write_seqlock(&vnode->cb_lock);
 
-	if (call->cb_break == afs_cb_break_sum(vnode, cbi)) {
+	if (!afs_cb_is_broken(call->cb_break, vnode, cbi)) {
 		cb_expiry = xdr_to_u64(xdr->expiration_time);
 		do_div(cb_expiry, 10 * 1000 * 1000);
 		vnode->cb_version	= ntohl(xdr->version);