From: Pavel Shilovsky pshilov@microsoft.com
commit 86a7964be7afaf3df6b64faaa10a7032d2444e51 upstream.
There is a race between a system call processing thread and the demultiplex thread when mid->resp_buf becomes NULL and later is being accessed to get credits. It happens when the 1st thread wakes up before a mid callback is called in the 2nd one but the mid state has already been set to MID_RESPONSE_RECEIVED. This causes NULL pointer dereference in mid callback.
Fix this by saving credits from the response before we update the mid state and then use this value in the mid callback rather then accessing a response buffer.
Cc: Stable stable@vger.kernel.org Fixes: ee258d79159afed5 ("CIFS: Move credit processing to mid callbacks for SMB3") Tested-by: Frank Sorenson sorenson@redhat.com Reviewed-by: Ronnie Sahlberg lsahlber@redhat.com Signed-off-by: Pavel Shilovsky pshilov@microsoft.com Signed-off-by: Steve French stfrench@microsoft.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org
--- fs/cifs/cifsglob.h | 1 + fs/cifs/connect.c | 15 +++++++++++++++ fs/cifs/smb2ops.c | 8 +------- 3 files changed, 17 insertions(+), 7 deletions(-)
--- a/fs/cifs/cifsglob.h +++ b/fs/cifs/cifsglob.h @@ -1524,6 +1524,7 @@ struct mid_q_entry { struct TCP_Server_Info *server; /* server corresponding to this mid */ __u64 mid; /* multiplex id */ __u16 credits; /* number of credits consumed by this mid */ + __u16 credits_received; /* number of credits from the response */ __u32 pid; /* process id */ __u32 sequence_number; /* for CIFS signing */ unsigned long when_alloc; /* when mid was created */ --- a/fs/cifs/connect.c +++ b/fs/cifs/connect.c @@ -905,6 +905,20 @@ dequeue_mid(struct mid_q_entry *mid, boo spin_unlock(&GlobalMid_Lock); }
+static unsigned int +smb2_get_credits_from_hdr(char *buffer, struct TCP_Server_Info *server) +{ + struct smb2_sync_hdr *shdr = (struct smb2_sync_hdr *)buffer; + + /* + * SMB1 does not use credits. + */ + if (server->vals->header_preamble_size) + return 0; + + return le16_to_cpu(shdr->CreditRequest); +} + static void handle_mid(struct mid_q_entry *mid, struct TCP_Server_Info *server, char *buf, int malformed) @@ -912,6 +926,7 @@ handle_mid(struct mid_q_entry *mid, stru if (server->ops->check_trans2 && server->ops->check_trans2(mid, server, buf, malformed)) return; + mid->credits_received = smb2_get_credits_from_hdr(buf, server); mid->resp_buf = buf; mid->large_buf = server->large_buf; /* Was previous buf put in mpx struct for multi-rsp? */ --- a/fs/cifs/smb2ops.c +++ b/fs/cifs/smb2ops.c @@ -151,13 +151,7 @@ smb2_get_credits_field(struct TCP_Server static unsigned int smb2_get_credits(struct mid_q_entry *mid) { - struct smb2_sync_hdr *shdr = (struct smb2_sync_hdr *)mid->resp_buf; - - if (mid->mid_state == MID_RESPONSE_RECEIVED - || mid->mid_state == MID_RESPONSE_MALFORMED) - return le16_to_cpu(shdr->CreditRequest); - - return 0; + return mid->credits_received; }
static int