ksmbd: fix race condition with fp

fp can used in each command. If smb2_close command is coming at the
same time, UAF issue can happen by race condition.

                           Time
                            +
Thread A                    | Thread B1 B2 .... B5
smb2_open                   | smb2_close
                            |
 __open_id                  |
   insert fp to file_table  |
                            |
                            |   atomic_dec_and_test(&fp->refcount)
                            |   if fp->refcount == 0, free fp by kfree.
 // UAF!                    |
 use fp                     |
                            +
This patch add f_state not to use freed fp is used and not to free fp in
use.

Signed-off-by: Namjae Jeon <[email protected]>

smb2pdu.c

@@ -3564,8 +3564,10 @@ int smb2_open(struct ksmbd_work *work)
 #endif
 	ksmbd_revert_fsids(work);
 err_out1:
-	if (!rc)
+	if (!rc) {
+		ksmbd_update_fstate(&work->sess->file_table, fp, FP_INITED);
 		rc = ksmbd_iov_pin_rsp(work, (void *)rsp, iov_len);
+	}
 	if (rc) {
 		if (rc == -EINVAL)
 			rsp->hdr.Status = STATUS_INVALID_PARAMETER;

vfs_cache.c

@@ -357,6 +357,9 @@ static void __ksmbd_close_fd(struct ksmbd_file_table *ft, struct ksmbd_file *fp)
 
 static struct ksmbd_file *ksmbd_fp_get(struct ksmbd_file *fp)
 {
+	if (fp->f_state != FP_INITED)
+		return NULL;
+
 	if (!atomic_inc_not_zero(&fp->refcount))
 		return NULL;
 	return fp;
@@ -406,15 +409,20 @@ int ksmbd_close_fd(struct ksmbd_work *work, u64 id)
 		return 0;
 
 	ft = &work->sess->file_table;
-	read_lock(&ft->lock);
+	write_lock(&ft->lock);
 	fp = idr_find(ft->idr, id);
 	if (fp) {
 		set_close_state_blocked_works(fp);
 
-		if (!atomic_dec_and_test(&fp->refcount))
+		if (fp->f_state != FP_INITED)
 			fp = NULL;
+		else {
+			fp->f_state = FP_CLOSED;
+			if (!atomic_dec_and_test(&fp->refcount))
+				fp = NULL;
+		}
 	}
-	read_unlock(&ft->lock);
+	write_unlock(&ft->lock);
 
 	if (!fp)
 		return -EINVAL;
@@ -630,6 +638,7 @@ struct ksmbd_file *ksmbd_open_fd(struct ksmbd_work *work, struct file *filp)
 	fp->tcon		= work->tcon;
 	fp->volatile_id		= KSMBD_NO_FID;
 	fp->persistent_id	= KSMBD_NO_FID;
+	fp->f_state		= FP_NEW;
 	fp->f_ci		= ksmbd_inode_get(fp);
 
 	if (!fp->f_ci) {
@@ -651,6 +660,14 @@ struct ksmbd_file *ksmbd_open_fd(struct ksmbd_work *work, struct file *filp)
 	return ERR_PTR(ret);
 }
 
+void ksmbd_update_fstate(struct ksmbd_file_table *ft, struct ksmbd_file *fp,
+			 unsigned int state)
+{
+	write_lock(&ft->lock);
+	fp->f_state = state;
+	write_unlock(&ft->lock);
+}
+
 static int
 __close_file_table_ids(struct ksmbd_file_table *ft,
 		       struct ksmbd_tree_connect *tcon,

vfs_cache.h

@@ -60,6 +60,12 @@ struct ksmbd_inode {
 	__le32				m_fattr;
 };
 
+enum {
+	FP_NEW = 0,
+	FP_INITED,
+	FP_CLOSED
+};
+
 struct ksmbd_file {
 	struct file			*filp;
 	u64				persistent_id;
@@ -112,6 +118,7 @@ struct ksmbd_file {
 	/* if ls is happening on directory, below is valid*/
 	struct ksmbd_readdir_data	readdir_data;
 	int				dot_dotdot[2];
+	unsigned int			f_state;
 };
 
 static inline void set_ctx_actor(struct dir_context *ctx,
@@ -160,6 +167,8 @@ int ksmbd_init_global_file_table(void);
 void ksmbd_free_global_file_table(void);
 int ksmbd_file_table_flush(struct ksmbd_work *work);
 void ksmbd_set_fd_limit(unsigned long limit);
+void ksmbd_update_fstate(struct ksmbd_file_table *ft, struct ksmbd_file *fp,
+			 unsigned int state);
 
 /*
  * INODE hash