CIFS: Fix too big maxBuf size for SMB3 mounts

SMB3 servers can respond with MaxTransactSize of more than 4M
that can cause a memory allocation error returned from kmalloc
in a lock codepath. Also the client doesn't support multicredit
requests now and allows buffer sizes of 65536 bytes only. Set
MaxTransactSize to this maximum supported value.

Cc: stable@vger.kernel.org # 3.7+
Signed-off-by: Pavel Shilovsky <piastry@etersoft.ru>
Acked-by: Jeff Layton <jlayton@redhat.com>
Signed-off-by: Steve French <smfrench@gmail.com>

3 files changed, 10 insertions, 11 deletions

diff --git a/fs/cifs/smb2glob.h b/fs/cifs/smb2glob.h
index c38350851b08..bc0bb9c34f72 100644
--- a/fs/cifs/smb2glob.h
+++ b/fs/cifs/smb2glob.h
@@ -57,4 +57,7 @@
 #define SMB2_CMACAES_SIZE (16)
 #define SMB3_SIGNKEY_SIZE (16)
 
+/* Maximum buffer size value we can send with 1 credit */
+#define SMB2_MAX_BUFFER_SIZE 65536
+
 #endif  /* _SMB2_GLOB_H */
diff --git a/fs/cifs/smb2ops.c b/fs/cifs/smb2ops.c
index 757da3e54d3d..192f51a12cf1 100644
--- a/fs/cifs/smb2ops.c
+++ b/fs/cifs/smb2ops.c
@@ -182,11 +182,8 @@ smb2_negotiate_wsize(struct cifs_tcon *tcon, struct smb_vol *volume_info)
         /* start with specified wsize, or default */
         wsize = volume_info->wsize ? volume_info->wsize : CIFS_DEFAULT_IOSIZE;
         wsize = min_t(unsigned int, wsize, server->max_write);
-        /*
-         * limit write size to 2 ** 16, because we don't support multicredit
-         * requests now.
-         */
-        wsize = min_t(unsigned int, wsize, 2 << 15);
+        /* set it to the maximum buffer size value we can send with 1 credit */
+        wsize = min_t(unsigned int, wsize, SMB2_MAX_BUFFER_SIZE);
 
         return wsize;
 }
@@ -200,11 +197,8 @@ smb2_negotiate_rsize(struct cifs_tcon *tcon, struct smb_vol *volume_info)
         /* start with specified rsize, or default */
         rsize = volume_info->rsize ? volume_info->rsize : CIFS_DEFAULT_IOSIZE;
         rsize = min_t(unsigned int, rsize, server->max_read);
-        /*
-         * limit write size to 2 ** 16, because we don't support multicredit
-         * requests now.
-         */
-        rsize = min_t(unsigned int, rsize, 2 << 15);
+        /* set it to the maximum buffer size value we can send with 1 credit */
+        rsize = min_t(unsigned int, rsize, SMB2_MAX_BUFFER_SIZE);
 
         return rsize;
 }
diff --git a/fs/cifs/smb2pdu.c b/fs/cifs/smb2pdu.c
index a3f7a9c3cc69..860344701067 100644
--- a/fs/cifs/smb2pdu.c
+++ b/fs/cifs/smb2pdu.c
@@ -413,7 +413,9 @@ SMB2_negotiate(const unsigned int xid, struct cifs_ses *ses)
 
         /* SMB2 only has an extended negflavor */
         server->negflavor = CIFS_NEGFLAVOR_EXTENDED;
-        server->maxBuf = le32_to_cpu(rsp->MaxTransactSize);
+        /* set it to the maximum buffer size value we can send with 1 credit */
+        server->maxBuf = min_t(unsigned int, le32_to_cpu(rsp->MaxTransactSize),
+                               SMB2_MAX_BUFFER_SIZE);
         server->max_read = le32_to_cpu(rsp->MaxReadSize);
         server->max_write = le32_to_cpu(rsp->MaxWriteSize);
         /* BB Do we need to validate the SecurityMode? */