[PATCH AUTOSEL for 4.9 057/156] afs: Deal with an empty callback array

[alexander . levin]

From: Marc Dionne <marc.dionne@xxxxxxxxxxxx>

[ Upstream commit bcd89270d93b7edebb5de5e5e7dca1a77a33496e ]

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@xxxxxxxxxxxx>
Signed-off-by: Sasha Levin <alexander.levin@xxxxxxxxxxx>
---
 fs/afs/cmservice.c | 11 +++++------
 fs/afs/internal.h  |  5 ++++-
 2 files changed, 9 insertions(+), 7 deletions(-)

diff --git a/fs/afs/cmservice.c b/fs/afs/cmservice.c
index d764236072b1..85cc6ecddcbb 100644
--- a/fs/afs/cmservice.c
+++ b/fs/afs/cmservice.c
@@ -165,7 +165,6 @@ 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);
@@ -227,9 +226,9 @@ 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++;
@@ -237,14 +236,14 @@ 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++);
diff --git a/fs/afs/internal.h b/fs/afs/internal.h
index 535a38d2c1d0..6961f6175529 100644
--- a/fs/afs/internal.h
+++ b/fs/afs/internal.h
@@ -105,7 +105,10 @@ struct afs_call {
 	unsigned		request_size;	/* size of request data */
 	unsigned		reply_max;	/* maximum size of reply */
 	unsigned		first_offset;	/* offset into mapping[first] */
-	unsigned		last_to;	/* amount of mapping[last] */
+	union {
+		unsigned	last_to;	/* amount of mapping[last] */
+		unsigned	count2;		/* count used in unmarshalling */
+	};
 	unsigned char		unmarshall;	/* unmarshalling phase */
 	bool			incoming;	/* T if incoming call */
 	bool			send_pages;	/* T if data from mapping should be sent */
-- 
2.11.0