afs: Deal with an empty callback array

Servers may send a callback array that is the same size as
the FID array, or an empty array.  If the callback count is
0, the code would attempt to read (fid_count * 12) bytes of
data, which would fail and result in an unmarshalling error.
This would lead to stale data for remotely modified files
or directories.

Store the callback array size in the internal afs_call
structure and use that to determine the amount of data to
read.

Signed-off-by: Marc Dionne <marc.dionne@auristor.com>

1 files changed, 5 insertions, 6 deletions

diff --git a/fs/afs/cmservice.c b/fs/afs/cmservice.c
index 2edbdcbf6432..3062cceb5c2a 100644
--- a/fs/afs/cmservice.c
+++ b/fs/afs/cmservice.c
@@ -187,7 +187,6 @@ static int afs_deliver_cb_callback(struct afs_call *call)
         struct afs_callback *cb;
         struct afs_server *server;
         __be32 *bp;
-        u32 tmp;
         int ret, loop;
 
         _enter("{%u}", call->unmarshall);
@@ -249,9 +248,9 @@ static int afs_deliver_cb_callback(struct afs_call *call)
                 if (ret < 0)
                         return ret;
 
-                tmp = ntohl(call->tmp);
-                _debug("CB count: %u", tmp);
-                if (tmp != call->count && tmp != 0)
+                call->count2 = ntohl(call->tmp);
+                _debug("CB count: %u", call->count2);
+                if (call->count2 != call->count && call->count2 != 0)
                         return -EBADMSG;
                 call->offset = 0;
                 call->unmarshall++;
@@ -259,14 +258,14 @@ static int afs_deliver_cb_callback(struct afs_call *call)
         case 4:
                 _debug("extract CB array");
                 ret = afs_extract_data(call, call->buffer,
-                                       call->count * 3 * 4, false);
+                                       call->count2 * 3 * 4, false);
                 if (ret < 0)
                         return ret;
 
                 _debug("unmarshall CB array");
                 cb = call->request;
                 bp = call->buffer;
-                for (loop = call->count; loop > 0; loop--, cb++) {
+                for (loop = call->count2; loop > 0; loop--, cb++) {
                         cb->version     = ntohl(*bp++);
                         cb->expiry      = ntohl(*bp++);
                         cb->type        = ntohl(*bp++);